Bi-amping the fronts means having 13 amps available for a 7.1.4 configuration. As
@William Lemmerhirt mentioned, using 7 ear level speakers really requires at least 4 height speakers. The surround back speakers will be the most expendable in an atmos setup and 5.1.4 would be more desirable than 7.1.2.
I just don’t see bi-amping as necessary at all especially when using two subwoofers. I’m curious about the crossover and subwoofer settings with Onkyo. Again, wanting 7.1.4 while bi-amping the fronts requires 13 amps. Add Zone 2 and Zone 3 and 17 amps are required to power it all. It’s a tall order.
Some newer Denon/Marantz models featuring 2CH Playback settings AND Directional Subwoofer settings may eliminate the need some may feel they have for bi-amping front speakers. The fronts can be run as Large using the LFE+Main subwoofer setting for 2ch signals in Direct or Stereo mode after being set as Small in the initial setup using crossovers for multichannel signals using surround sound modes.
If budget permits, the Denon A1H really is the only all in one box solution for powering a 7.1.4 Main Zone and also Zone 2 and Zone 3. I wouldn’t give up Zone 3 to bi-amp the fronts. There shouldn’t be any bass issues crossing the fronts at 80Hz and using two subs and not bi-amping. There also shouldn’t be an issue using fronts as Large with LFE+Main for 2ch signals in Direct or Stereo mode without bi-amping and using 2 subs. Using 4 subs will get the most out of the Directional Subwoofer settings when playing multichannel signals.