The only X.X.4 Atmos Pioneer, Yamaha, Denon, Marantz models currently available from 2014 are MSRP $1500+. Not likely to see any 2015 models offering more than X.X.2 as they are all 7CH models none of which are likely to be expandable to 9CH which would be required to offer X.X.4.
If these 5.1.2 (or 7.1) receivers had proper speaker position calibration and pre-outs, you could buy two of the 500$ models and daisy-chain them.
There is no technical reason you couldn't have 7 channels at one level and 7 independent height channels.
You can enable Atmos rendering with only the bed speakers plugged in / enabled, right? No reason to not render as many channels as you like, as long as your hdmi inputs / outputs are forwarding Atmos data to the next AVR in the HDMI chain. But that's assuming they get their thumbs out and actually provide proper 3D speaker placement calibration. You should be able to place your speakers whereever you want, however many you want. Sound waves superimpose making sound additive. I'm trying to understand if you had two identical Atmos systems going on at the same time, but calibrated to slightly (or very) different positions, with 1/2 the volume, why that wouldn't work just as well as a single Atmos renderer that only thinks you have X number of speakers.
Not sure how well that'd work for DSU though. Maybe it would. It would make an interesting experiment. Unfortunately apparently even the Yamahas don't have accurate/arbitrary 3D speaker positioning for all their channels.
