For best results you will want to be able to live monitor in 5.1. This implies a sound "card" with at least 6 outputs, and someplace to plug them in.
An inexpensive device that works will on OSX (core audio, no driver needed) is an esi gigaport hd.
http://www.esi-audio.com/products/gigaporthd/ that will get you 6 chs out at up to 48 Khz 24 bits, but not higher sample rates (it drops to stereo at 96 Khz).
Then the next question is what do you plug that into? If your HT is close by, and has spam ins (and does bass management on the spam ins) your set. Or if you have (decent sounding) powered 5.1 PC speakers.
If your HT does have spam ins but does not do bass management (most are in this category) you can add a bass managment AU plugin to your layout.
If your HT doesn't have spam ins you will want to get a creative dts 610 (no longer made and getting scarce) which can take spam ins and convert to DTS SPDIF on the fly:
http://www.amazon.com/dp/B002651ZEM/?ta ... cp1suwwl_bGlad your happy with your results so far. That's what it's all about.