Again, the pre out doesn't clip at 1.4 Vrms (the internal power amp will be clipping at that point). Take a look of the center channel of the X3600H, that obviously has the internal power connected:
That's almost as good as the AV7705 (a so called "separate" preamp processor.
Note that the dash board of the AV7705 measurements show about 4 V but that's XLR, had Amir used RCA for that measurement, it would have been 2 V and SINAD would have been about the same, again, as the AVR-X3600H that is an AVR, therefore internal amps would be "clipping" and degrading the SINAD at pre out.
So I really wouldn't worry about your center channel, unless you will be pusing the Purifi amp to output almost 400 W average (800 W peak) into 8 Ohms and you can hear the difference between 75 dB and 95 dB SINAD (I know I can't..).
- Omitted -
Denon/Marantz Preamp output limits and Gain Structure
I'm becoming less convinced over time that the 1.4V preamp limit is based on the associated power amplifier channel clipping. There may be a lot we don't understand about the Denon/Marantz AVR's/AVP's. This is a good subject for some future thread. Some items to consider concerning the 1.4V level and also the D/M gain structure.
(1) 1.4V into an amp with a 28.2x gain gives 39.5V or a rail voltage of 55.4V plus some extra for drops in the power stage. 39.5V into 8 ohms is about 200W.
With five channels driven the power output per channel may drop to 100W. This requires an output of 28.3Vrms with 39.6V as the rail voltage. At a gain of 28.2x the input from the preamp would be about 1V. Does this really mean that the preamp channels now essentially clip at 1V output since the associated undriven power amplifier stage will now clip at 28.3V output due to the drop in the rail voltage due to the load on the other channels?
This drop in preamp clean output suggests that the distortion performance of the preamp outputs will be modulated by the output of the power amplifier channel. This seems a mess and unacceptable. The 1.4Vrms value is such a common value in D/M gear that I wonder if it is set by gear and not determined by the clipping level.
(2) Based on my measurements of the AV7705, a 0dbFS input with 1.4V XLR output results in about -96dB THD and about -95dB THD+N. -6dBFS input with 1.4V XLR output with the volume control increased by +6dB results in about -104dB THD and -99 THD+N. Does Denon/Marantz make use of this relationship in the actual operation of the AVR's/AVP's? Output levels in the 1V to 2V range produce similar relationships in output performance.
Products like RME DAC's switch resistors to change gain to a take advantage of this sort of relationship. D/M could reduce the digital output in the DAC IC by 6dB and increase the volume control setting (internally, not seen by the user) by 6dB to get the better measurements noted above. The relatively low preamp output levels reported by many for D/M gear used in home theaters of -10dB to -25dB would allow a lot of room for adjusting gain to maximize performance.