Agreed 100%, that's why I disagree with Amir labelling the 75 to 76 dB SINAD "clip". Think about this, if 75 dB SINAD is "clip" what is point for many high end power amps claiming 200 W 8 ohms at 1%, 1% is only 60 dB SINAD.
Denon and Marantz's own specs are based on 0.05% THD+N, that is 66 dB SINAD for the 4000 and above (Denon), 7000 and above (Marantz) series and 0.08%, that is 62 dB SINAD for the 3000 Denon and 6000 Marantz series. So why are we even debating whether 75 dB SINAD is a clipping problem?
Ask the many AV7705 owners if they are concerned about the 75 dB SINAD. Most, if not all, chose the AV7705 instead of the SR7015 or Denon AVR-X4700H because they are audiophile who believe separates are better, don't you think?
No, first of all, you have to understand it is a fact that the output range of the Denon preamp is not 0 to 1.4 V, but more like 0 to 4 Vrms. That's a fact, you can buy the service manual and/or download the datasheet of the preamp vol chip and see for yourself:
You can see that their specs show 4.2 Vrms rated.
Even if it is (that it isn't) 0-1.4V, the Denon is not going to send a lower voltage to the pre out because the output voltage is dependent on the input voltage and gain:
That is, Vout = Vin X Gain, so the output voltage would be the same in both cases, only that if the maximum is only 1.4 V, then at higher input voltage the output voltage will be clipping so while it will still go up, but it will no longer be linear, as it will be flat topped, the definition of clipping.
The important thing is, to understand that in non preamp mode, performance suffers but not the maximum output. And while performance suffers, 75 dB SINAD (or even 65 dB) is likely below the threshold of audibility of most AVR users. But of course we all want 120 dB SINAD regardless.
Yes that is correct, that's is why Amir recommended that if you are going to use the Denon AVR (also Marantz AVR and their AVPs such as the AV7705), you should try and get power amps that has higher gain, for the cleanest possible pre out voltage. But it is not the same as saying those AVRs, in non preamp mode cannot drive amps such as the buckeye NC502MP to their maximum output because it can, only that you won't get 95 to 100 dB SINAD.
I hope by now you understand the difference of saying 1.4 V as the maximum and saying 1.4 V is not the maximum but it is the highest output at about 100 dB SINAD, at higher voltage, SINAD will drop gradually, to about 76 dB at 2 V. I highly doubt you can hear the difference between 76 dB SINAD and 96 dB SINAD. And again, it only dropped to 76 dB at 2 V, at say 1.7 to 1.75 V, it looks more like 80 dB SINAD, that's 0.01%
At 2 V, even the 26 dB gain buckeye amp can be driven to output 200 W 8 ohms, or 400 W 4 ohms.
No, that is not the "only measurable difference", it is more likely either your Anthem AVR has a higher gain for the subwoofer channel, or if you use RC, after running ARCG, you are getting more boost at that frequency than Audsyssey did, or a combination of both. It could also be that you had some settings on you Denon messed up. Without looking through all the settings, and/or taking some measurements, we can only speculate.
I have been using external amps only for years and I have never experience such issue with my SVS subs. They would wake up even when I listened at relatively low volume. I normally listen to less than 70 dB average from 11 ft. I can't do any test now as I traded in my Denon for the Anthem.