This is just a second thought on the soundcard idea. Have you tried
Options,Preferences, Midi drivers, Synthesizer Sound Card? The Native
Instruments Bandstand Driver sounds much better than the others on my laptop
running Vista. Try the choices and see if you get better sound. Also many of
the GM2 instruments don't sound anything like the labels so go through and see
what you like. The best guitar sound I have is 25/1 Ukelele for example. 25/1
bears no resemblance to Ukulele. If you are not too critical and work around
some of the sounds that are not realistic at all, like banjo, you may find that
you can get by without additional investments.