Do the Marantz HDAMs also cause extra distortion (without any improvements) in their power amps and 2 channel products too?
If you mean the likes of the PM8006, PM-10 integrated amps, you can reference Gene's review of the older PM-11S3. Power amps don't have HDAMs as they are only used on preamps and integrated amps.
It does look like the distortions level would be closer to that of the Denon AVRs and the Marantz AV8805, but much better than the SR6014's. The two graphs are actually quite similar, they look flipped because AH uses THD+N in %, while ASR's are in SINAD, that is the inverse of THD+N, if expressed in dB they will be exactly the same numerically but THD+N would be -ve.
For comparison, at 2 V, the PM-11S2's THD+N is about 0.005%, that is about SINAD 86 dB, vs the SR6014's 0.0097%, that is SINAD 80.5 dB.
The PM series, especially the expensive PM-11S1/S2/S3 and the newer PM-10, do have much more robust HDAMs that should add very little distortions and I am sure they have benefits, in terms of impedance buffering anyway, though from the graph the effects do seem obvious.
Review: The Marantz PM-11S3 Integrated Amplifier is rated at 100 watts/channel. It exceeds its specifications and sounds and looks great doing it. A true audiophile product with prideful ownership.
www.audioholics.com
This is a review and detailed measurements of the Marantz SR6014 Audio/Video Receiver. It was purchased new and kindly drop shipped to me. It costs US $1,500. The SR6014 looks just like all the other Marantz AV products: I must say, as iconic as the round display is, coming from testing...
www.audiosciencereview.com