My flex digi is arriving in a few days, and I too have such a setup: avr and streamer sharing the mains and two subs.
Regarding subs for avr: avr preouts to flex, one preset using subs only in mono( while music setup is 2.2,stereo subs, as I had them up to now - lfe in from avr, neutrik from stereo amp).
For avr, intend to set subs to flat response, and let audyssey xt32 do DEQ afterwards.
How should I do the tweaking and setup, as obviously I want to set gains on subs and never touch anything again. Also, I run them in ~70 degrees phase, as that got me the best, or the least worse, response. That should go to 0 before I start?
Initially, I would go with mini dsp plugin and go for dirac only if I find it too much for me or it really is that much better.