TTS-1 captures midi songs very good, I have a Mac now waiting for Sonar Mac (PC died).. Need to play some midi backing tracks urgently.. Any suggestion? Any other alternatives?

Does garage band do midi - I think its free for Mac?

I'm not a Mac guy, but I'm pretty sure you'll need to run Windows using Boot Camp or a virtual machine like VirtualBox.
 
FWIW, there are general midi sounds built into Mac OS, but I'm guessing you'll need a way to record them? You can buy GarageBand for $5 if you don't already have it.
 
This looks dated, but may be helpful with accessing GM instruments from within GarageBand.

Garageband might be worth a try. Logic's much better, being a full DAW and relatively cheap compared to most.

Downloading a free trial demo of one of the established DAWs like S1 or Reaper might work as well.