Ok I did some sleuthing. Is this the file you guys were using?
SDHC.777.cab.zip

If not I would try this cab. Here is the thread that I found it in:
xda-developers - View Single Post - Sandisk 6GB Micro SDHC Shipping!

Which referred to this thread on PPCGeeks.com:
Micro SD Storage Card - Page 3 - PPCGeeks

In case you don't want to read the thread this worked for someone who used a Sprint Mogul that did not have any luck before that. If the older driver worked for the 4GB, I fell comfortable saything that this new one should work for the 6GB.

I would also strongly suggest more of you to get acquainted with what's going on in WM6 over at xda-developers.com and ppcgeeks.com and others sites. Many of their hacks/addons/mods will work on any WM6 Pro phone. With just a few people bringing back information from other places it will help out a lot of people.