Its difficult to judge, but comparing several "subjective reviews" the Integra and the Onkyo are supposed to sound almost the same, whilst the Pioneer seems to sound somewhat different, but in a negative way...This is interesting....
One would assume that the preamp mode requires actual physical hardware (a relay switch) rather than being mere software/firmware.
So this implies a hardware difference between the RZ70 & DRX8.4 (and possibly the LX805)... if the boards are different, then we will need to pay attention for/to future bench tests of the other siblings, as their performance may differ!
Hard to judge subjectively...