It's pretty amazing that for all the things Powertracks can do, they still only ask $49, and you can download it and start working, and they send you the cd and manual by mail.
It certainly holds up to the bigger names in software, but it's easier to work with. Don't let the screenshots scare you, you see almost all windows open, which in reality never happens. http://www.pgmusic.com/powertracks.htm
And if you buy Powertracks Pro, for only $20 more, you can get the Roland's VSC-3 Virtual Sound Canvas with 128 polyphony, 546 sounds + 15 drum sets and the ability to render a *.WAV file right from a MIDI file. http://www.pgmusic.com/rolandvs.htm
Plus you get an Unconditional 30-Day Money Back Guarantee in case you don't like it.
In the midi setup, you can set the WK3500 to be used as a midi master kb, without using it's own sounds.
Have a nice day