The TOS rom that loads on start, won't accept anything larger than 2.5megabytes (error 140). The card doesn't respond to anything in the $1ff4-1fff range when mapped (last bank mapped remains as is). So I have no idea why the mention 8megabyte rom support on all the TE sites. Krikzz mentioned that he thought it would load up to a 4megabyte rom, but even if I got past error 140 (probably rom size to big) - there doesn't seem to be a way to even access it. A shame really, 'cause I made a post about this before the card was released - asking for the full SF2 mapper range. Oh well.
The other thing of interest; Populous works. Well, the original rom works. My custom rom with the same unlock codes - doesn't get access to the extended ram. Either I missed something or the TOS loader is specifically enabling that support based on some sort of rom ID process.