GuruGeek2002,
The expansion slot on the 6k is solely for use with the Expansion Jacket.
The cable you are referring to hooks up to the proprietary Sharp i/o, (the same port that the "Death Star" docking cradle uses), and can be used with either a sharp i/o - serial (com port) cable to use it with serial devices such as external modems and gps devices or with a sharp i/o - usb cable that allows the unit to be used as a usb client, this enables the unit to be synch'd instead of using the docking cradle and if hooked to a usb port that is powered will also allow the unit to charge itself. In case all this sounds familiar, yes it is the exact identical port that every Zaurus product has used back to the SL-5x00 series and operates exactly the same way.
The usb host port, (the tiny usb port at the bottom right of your unit),on the other hand uses a rather neat little chipset that detects if it is connected to another usb host and if it recognizes that has happened it switches itself to become a usb client instead, if another host is not detected it operates in usb host mode. This actually means you have two methods of using your Z6k as a usb client, ironically however the syncing software only works with the sharp i/o to usb method. I have not seen any post that anyone has found a use for using the usb port as a usb client to date. It's nifty that it operates that way but completely useless so far. USB devices that are known to work with the 6000's built in usb host are usb hubs, any usb memory device that can work with windows 2k or XP without drivers- this includes usb pens etc., some usb multi card readers, usb keyboards (a few keys need remapped), SOME usb external cd-roms, SOME usb external floppy drives, usb external Hard Drives of both the 2.5 and 3.5 variety, many usb cameras and mp3 players (ones that show up in win2k and XP without drivers) NOTE: they are just useful as storage and cannot be used to take pictures through them or play mp3's through them etc.), and usb wireless and wired network cards (the 6000L's own internal wireless card runs on the usb host bus). Some usb devices that are known to NOT work currently but have projects currently in development to either allow them to be used with Linux in general or with the Zaurus 6k's in particular are USB camera's (such as web cam's), usb mice, usb Zip drives, usb floppies, and usb GPS devices.
As for the sharp i/o port itself, if you own one you will discover that there is an additional sharp i/o port on the expansion jacket. Apparently, (I have not tried it myself), it's purpose is to allow the user to use the extra port with a serial or usb cable while it is docked. There has been some debate as to whether or not this actually works as all evidence points to the fact that the Zaurus 6k itself sees both ports as the same resource from a serial perspective. My only conclusion is that its use would be limited to using the extra port as a serial device when docked since the dock is using the usb client portion of the port interface. Or possibly using a sharp i/o usb cable in one port and using a sharp i/o - serial cable in the expansion jacket or vice versa simultaneously.
The SD port will work with MMC or SD memory cards and the hardware also supports the new SDIO specs for using SD wifi cards as well. The Sharp rom and kernel however does not implement this feature and since this production line has been dropped it surely never will. It is possible that community built roms such as Cacko and pdaXrom etc. could enable this in the future, but that is doubtful since the software code for the SDIO slot is privately owned and proprietary and they would have to purchase the liscence to use it. It is possible that they could reverse engineer the code but every current Rom team has openly stated that they currently do not have the money to back this, nor the resources to reverse engineer it from scratch. It is noted that the existence of SDIO hardware support and the lack of kernel/software support is shared with the C860 device.
The CF port will support all known Compact Flash memory formats and is also PCMCIA aware at both the hardware and kernel levels. This means that if you buy a cf-pcmcia adapter any pcmcia card should work as long as it is 3.3v and 16 bit, Several pcmcia modems, wifi, and network cards are known to work as well as toshiba pcmcia 1-5gb hard drives. The catch is of course that there are many devices that we do not have drivers for so whether your GPS, Barcode Reader, Bluetooth CF adapter etc. may work or not is a different story. But again this has not changed and these exact same support and limitations are identical to the CF slots of all models back to the SL-5x00 series. (The fact that you can use a CF-pcmcia adapter with the 5gb Toshiba PCMCIA cards on the SL-5x00 models is not a very well known one. I personally use one with my 5500 and it works perfectly, it just eliminates the ability to use a CF Wifi card at the same time- a problem you will never have with your 6000!) Some GPS, Barcode Readers, and Bluetooth cards work currently and much work is being done as you read this to expand the Bluetooth capability of the 6k. One major class of CF cards that does NOT work currently is the VGA Monitor out Card. This same limitation exists for all Zaurii presently, and since the large scale demand is not present for this option coupled with the bandwidth limitations of the CF technology itself will probably inhibit these models from ever having the capability. There is one VGA CF card on the market that will display certain graphic images (jpegs I think) does work for some of the earlier Zaurii but I have not seen a single post from anyone that has accomplished it with a 6k. Since all it will display is images in that graphic format its benefit is extremely limited. NOTE: if using the expansion jacket the user will have a second CF slot that appears in your resource listings as CF2. The specs on this second CF slot is identical to the primary CF slot. There seems to be some debate as to whether the CF slot in the expansion jacket will work when the extra battery in the expansion jacket is depleted and the user is not plugged into a dc adapter. I have exhaustively tested this myself and have had no problems under any condition with the CF2 slot working as long as there was any charge left at all on either the primary or secondary battery. I attempted to get some help from other expansion jacket owners to test this issue more widely but was unable to get any assistance. Feel free to search the Forums here for more info or click on my posting name and view my prior posts on this subject.
One final word on the SD and CF slot with memory card usage. While the compatability of these slots with memory cards is similar to that of older Zaurii, memory throughput while both reading and writing is MUCH higher than the older SL-5x00's. This is probably as much the result of faster processors as it is to the newer SD/CF slot technology. The speed of the 6k is almost identical to the c7x0/c860 models. Regardless the achievable speed of both devices on the Zaurus does not even begin to approach current CF/SD theoretical bandwidth speeds (such as what you would see by using the same card in a desktop machine via a card reader.) There are numerous threads here on the ZUG that demonstrate that even with the newer cards reaching 32x-80x speeds and beyond that the top acheivable bandwidth in the 6000/C860 slots tops out at around 12x to 14x, having said that let me temper this by saying YMMV.
The only remaining port is the 2.5mm stereo sound jack. It will automatically sense whether you have inserted a pair of headphones, (you will have to use a an adapter to use your normal headphones or buy a pair that already have a 2.5mm plug), or if you have inserted a headphone/microphone set instead, (your cell phone set will work perfectly.)
Someone correct me if I'm wrong, but that should be a complete wrap of all the ports and what they are capable of.
Hope this helps!
-NeuroShock