SF
I use Vegas Audio for everything...i have the gadget labs hardware for a soundcard and can record 8 simultaneous tracks...I then do all my mixing and mastering (to the best of my sorry ability) in Vegas. From what I understand SF is good for final editing and mastering of a final mix. So, if you do all your multi-tracking in Sonar....and get a decent mix...you should be able to export the wav file (or whatever file type) into SF for final work. I still haven't really figured out the advantage of using SF if you already have something like Vegas or Sonar. Also, in regards to unlimited tracks...I assume Sonar has that capability. Vegas is only limited by how powerful your computer is...I've had over 20 tracks in one vegas file before...but am limited by how many effects are on the tracks...and how many tracks I'm playing back to monitor by my computer processor.