Well, your soundcard will still be needed in order ot get the sound out of your PC. To answer more seriously, no. You don't have much disadvantages. The only thing is that sometimes you get a longer latency time on a software than on a hardware sampler.

Can i use Gigasampler with my Yamaha RM1x?(hardware sequencer)[/QUOTE]

Yes you can. I've heard that the RM1X has a very neat sequencer and can control any external MIDI device. As long as you choose the MIDI IN port on gigastudio as an external controller, you should be able to control 16 channels of instruments of gigastudio.

Good luck man, and have fun