New HT - Separates Upgrade Options?

Building new house/7.2 HT with new 110" screen & tbd projector; bringing separates from old house, but need to be able to switch hdmi sources to proj and believe I want room correction for the 7.2. Plan for 50/50 HT/2-ch with edge to music quality, but also good video. Plan to retain Acoustic Zen Adagio (2 towers & center), McCormack DNA-500 stereo amp (balanced XLR inputs) and probably Proceed Amp-5 (125x5ch bal XLR; 10 yr old & needs new Pwr switch); current Lexicon MC-8 has no video switching. This setup in old house had more forward/bright presence; would like something more musical, but retain detail and imaging/soundstage.

Currently thinking about oppo-93, Martin Logan surrounds (FX-2 sides and Helos 20 rears) and tbd pre/pro with Bal XLR (<$3K price point). Heard good things about Audio Control M3 (Arcam 888 clone with unique features and good writeups), but would have to purchase used. Would appreciate your thoughts on pre-pro (options to consider), oppo-93 (better choice?) and if I decide to get new multi-channel amp, recommendations. Finally, other than seller history, any precautions for buying used on AudioGon?

Thanks in advance!