Don't feel bad, I did almost the exact same series of events when I first got my SL-C860 many months ago.
As long as you can get in the diag menu you can still do the nand restore (and the file provided in the previous link will put you back to sqaure 1 with the factory japan rom).
The SD or CompactFlash needs to be formatted FAT, unfortunatly I can't tell you how to do that on a linux machine. Once you have it formatted fat and copy the nand backup file to it (I bought a cheap multi reader from BestBuy to accomplish this) just follow the prompts and let it restore (it will take a LONG time compared to flashing so let it sit).
Once it is done you should be able to reboot and it will prompt you with all the same screens that it did the day you bought it