Yes that would be my opinion, based on calculations. Take a look of it this way:
- The voltage gain of the X8500H's internal amp is about 29 dB (a little less I think..)
- The Purifi amp's gain is about 26 dB (a little less iirc..)
So the difference in gain is 3 dB and that means at the same volume position, the Purifi amp will output half that of the Denon's internal amp's. You will have to either re-run Audyssey, or manually increase the level settings by about 3 dB.
Once level matched, all will be good, except the pre out voltage will be 3 dB higher than that of the other channels that are using the internal amps.
That does not matter much because as shown in the SINAD vs pre out voltage, the X8500H has almost no degradation when the pre out voltage increases to 2 V and beyond.
It will be the same even if you use a separate preamp processor, except in this case the Purifi amp will benefit from the balance outputs that will have 2X the voltage of the unbalance outputs. Many other power amps (such Marantz, Yamaha's, and Bryston's etc.) won't benefit from the 2X balanced output voltage the same way the Purifi's will, because their gains are 6 dB lower for balanced inputs.
Not true for most Brystons
Most Bryston power amplifiers such as the 4B3, 7B3, 9B3, 21B3 and previous models such as the 4BSST2, have a choice of 23db or 29dB gain for either SE or XLR inputs. The 6BSST2 offers three gain settings including 29dB. A simple switch setting on the back of the amplifier controls the gain. This means that the gain is not 6dB lower when using the XLR (balanced) inputs for the models above, if the 29dB gain setting is used.
A choice of gain settings is an excellent feature of these amplifiers. This choice should be understood and not ignored.