I have a Yamaha Aventage RX-A820 driver Revel M20's.
There is a obvious change in the sound when switching between
Pure and
Straight mode with no room correction and all tone controls flat. This is true of all receivers I have owned.
To me, that indicates that differences in sound quality can occur when additional circuitry and DSP processing is engaged. That is not good or bad since there are many benefits to DSP's.
There is no way to know for certain when a modern receiver, (Japanese in particular) are using DSP's. Selection options such as channel mapping, bi-amp, and base+LFE are likely handled by DSP processing.
If you can hear any difference between Pure (Pure Direct) and Direct/Straight modes on your receiver then you might consider why that is?
If you can hear such a difference, then consider that "AVR's sound the same except room correction" might not a complete assessment.
- Rich