Lag in QuartzAudio?

I'm running this program on XP with a Keystation 49 - finally sorted out the various start-up issues (no sound, couldn't record, etc.! ) that I see a lot of others have already posted....

So now I have the various voices accessible, and can record and playback. BUT - I still have two problems that I can't figure out (I'm a musician but new to music software) - anyone have ideas?

A) There is a serious lag from key depression to note sound - about half a second or so, which really throws off my tempo. Suggestions?

B) I set up four midi tracks and recorded the first voice as Harp. I then wanted to play back the Harp track while I recorded the second track with a different voice - Clarinet. However, when I set the second voice it changed in all four tracks, including the first one - so my harp became a clarinet. Is it possible to set four different (or more) voices, one in each track? It should be and I'm probably just missing a clicked button somewhere.

Thank you, everyone who's taken the time to comment and answer so far - this is more helpful than a lot of places I've looked! Hoping someone has ideas for my particular noobie questions.... :)

Judith