Best way to connect 2 preamps to 1 power amp

Man do you have this wrong. Your main preamplifier, I presume is the tube, you want to drive the fronts for surround sound via the Lexicon, therefore, you take the left and right surround sound outputs from the Lexicon and run them into the tube preamplifier into an aux in. Then you set the level of the tube preamps volume control with an SPL meter until all channels are at the same level, you then mark this level on the tube preamp as a reference level and everytime you place the Lexicion you must switch the tube preamp to aux in and set the tube preamps volume to the reference level you've noted before and voila you have a two channel tube preamp coupled to a Lexicon for surround.

Why not Email Bryston Canada and ask them about using the switch on the back for bal/rca. I'm sure they have had this come up before, I've wondered about this myself but have always used 2 systems.

Wow; you guys are awesome. I will try the suggestion from connecting the HT to one of the line-in of the tube. (I don't know I can do that). Also, I have some concern of switching over back & forth on the RCA/XLR as it will eventually become loose.
Thank you once again guys.

I also found out there is a by pass on the HT (Audio Refinement Pre-2DSP) whereas the tube doesn't (YS-Audio Symphonies Plus R). But I love the warmth on the tube. Is it of any use; please advice.

No use in this case because you want to send the processor through the tube pre instead of the other way around.