I have a Sonar X1 studio (and learing Pro Tools).
Are you using the latest drivers
for Win 7 64 bit, from Creative for the EMU? Creative Worldwide Support
Some OS functions and some sound functions are handled differently in Vista/Win 7 so how it worked in XP compared to Vista/Win 7 isn't a good comparision.
Also run the free DPC latency checker and see if anything shows up. DPC Latency Checker