If your computer setup is really fast with lots of RAM (at least 1.5-2GB), you could run GigaStudio 3 Orchestral version and that would give you nearly 20GB's of incredible sounds. Generally its best to run GigaStudio completely by itself so that conflicts don't occur and the processor isn't taxed much but running it with other software can be done on a really fast system. You'll need a hard drive that's bigger than the Giga Library file size (17GB+) if you want all the files to be resident. I'm certain you aren't going to complain about the quality of the Giga samples, especially if you've been using just a sound card and Clavinova. GigaStudio has some amazing samples and sound libraries and there are many synthesizer, orchestral, and drum libraries available.

Another option would be to run Reason, Reaktor, Pro 52, PPG Wave 2.V, or Arturia's CS-80V or Minimoog VST's. It all depends on the speed of your system as many of these programs can and will severely tax your CPU's speed.