First of all, 84.21 are not the latest drivers. I use 91.63 (from lv2go
) on my 6600GTs and even those are not the latest.
Second, make sure your LCD's DVI port actually supports computer input. My family has one HDTV with DVI input on it, but I read the manual it states it is not meant for use with the PC. On the other hand, I have another HDTV that does accept DVI input from the PC. So I can confirm that DVI output from 6600GT card really does work on some HDTVs, even with SLI enabled.
I hope this helps.