Ask around Audiogon. I always thought the Pro models were strictly XLR balanced. You do get a more supposedly cleaner full sound with XLR. Hence the Pro stamp. But when run unbalanced RCA its no diff than the ST version. Again this came from heresay rather than actually me hearing with my ears. So my thinking was if you get a Pro version and not run balanced it would be no diff than the ST version. I checked out the spec and both have the same spec. That does mean much. Send a note to Bryston. They are good with supplying info.

http://www.quadloft.com/hometheater- new HT