Since they don't make a separate PROCESSOR just for Atmos/DTSX, an AVP is as separate as you can get for HT.
Most audiophiles consider AVP a "separate".
But absolutely NOBODY considers a AVR as a "separate", especially when you throw in 11Ch or 13Ch of amps inside the same chassis.
Now if they started making a separate standalone processor for Atmos/DTSX, I would get that and use separate Preamps and Amps.