Originally Posted by Reggae_Mangle
Midi has no sounds of its own, so if the OP is going through the USB-Midi route, he will have to use a VST like GarageBand to output sound.
Connecting direct to the Mac using the line in is an option, but you're likely to get even worse sound than Garage Band, since the input is unlikely to be suitable for line level signals. As such, you'll have to deal with the sound distorting, or lower it to a level that's almost inaudible and then try to hike it up using a software preamp.
I can't connect direct to my Mac as I don't have a mic input, but if the sound quality is as bad as you say then it sounds like I'm not missing much.
Looks like the only viable option is using a Q3. I better get saving!
Thanks again for all your replies!