5.1 Mixing

 
 
If you want to mix in 5.1 surround you will need an interface with six analog outputs (unless you have digital powered):  A) 2 for right and left (mains); B)  2 L & R rear satellite monitors;  C) 1 for the center satellite monitor; 4) 1 more for a subwoofer (optional).
 
You could use any speakers, I guess, but if you are going to mix then I suggest reference monitors (which are sold individually).  As for USB interfaces, here are a few from cheap to expensive to much more expensive:  Behringer FCA610 ($200); TASCAM US-1800 ($200); Steinberg UR28M ($400); Roland Octa-Capture ($600); Roland Studio-Capture ($1000); Focusrite Scarlett 18i20 ($500); MOTU 828x ($850); MOTU 896mk3 Hybrid ($1000); MOTU 1248 ($1500); RME Fireface UC ($1400); RME Fireface UCX ($1600);RME Fireface 802 ($2000); and then there are those that are over $2000 from makers such as Antelope Audio, Prism Sound and Lynx (which may require additional hardware), just to name a few.  Some of the above mentioned interfaces have more than enough features for your needs, but I did list those that meet the minimum as well (eg, six analog outs). 
 
Kind regards,
 
Living Room Rocker

It looks I have a lot of good choices as far as a Audio Interface working with Sonar. The M-Track Eight from M-Audio is coming out soon too. It looks good.
 
It is the 5.1 monitoring system that is sticky. I have 2 powered Mackies for fronts and a Tannoy Sub which I have been using to mix in stereo. I filmed a concert while using Edius as my video editor. The stereo mix is done.
 
Sweetwater Music advised me (with my budget restrictions) to purchase all the same powered speakers for fronts and rears while using the same sub. (Not needing a Audiophile Quality Surround Level Controller) I was looking to buy 2 sets of the M-Audio AV-40s. But I will need a powered center speaker and most active speakers only sell in pairs. Any suggestions?

Give me some examples if have you time. I want them to be all the same, so we are talking 5 speakers. Did you check out the M-Audio AV-40s. That is my example of what I need.

Thanks for your response. 1/2 ton of examples would even be great! I am anxiously awaiting your suggestions!

My Mackies are almost 10 years old. They don't make them anymore. After reading your lastest response and doing some of my own research, I have come to the conclusion that I need to put some money together and do this right.
 
I think in the future somebody will introduce a USB or Firewire Amp with outputs to mix in 5.1 & 7.1 that will work with your DAW. I was being naive thinking I could buy 3 more powered speakers to work with my Mackies and Tannoy sub. Thanks for all your help.

Jeff:
 
I just switched from Mackie HR824s to Equator D5s. The D5 can be ordered in single speakers as well as pairs.
 
As much as I liked and was familiar with the Mackies (about 14 years), they were really too big for the room. The Equators are incredible in the midrange and are translating very well so far. I will be ordering 3 more in a month to set up 5.1.