I finally found a work-around for my problem that worked in "Howto: Oz 3.5.2 On Sl-6000l, sharing my experiences to date..."in the OZ section of the ROM forum. Pressing d and P while resetting brings up an extensive system menu with 4 pages, the last of which offers to restore a NAND. After figuring out that it wasn't recognising the NAND file because it was named syst0006.dbk-us and it expected syst0006.dbk, I restored the original Sharp NAND.
A suggestion: Could someone who knows the sl6000 well, publish a chart with all the basic key combos that concern the ROM, along with the combos for the other Zaurii for comparison. This would avoid a lot of confusion for new users as the info is scatterred around these forums. I looked very carefully for a solution to this common problem and I've had experience with other Zaurii, linux, other PDAs, and PCs in general.
Thanks Lardman for the help.