Now this is a teardown.

[Dundas]

He also does the AV7705

 

[valerianf]

Amazing teardown videos.
I like the power amplifier with its large transistors mounted on a tunnel heatsink.
You will never find that in an AVR.
The pre-amplifier is far less impressive with the board full of HDAM transistors.
This is the example of a marketing vaporware.

 

[KarVi71]

My Anthem MRX 300, has its power transistors mounted on a tunnel heatsink

As did the whole X00 series.

Later models do seem to have a more conventional heatsink.

 

[Jim85IROC]

The build quality of that amplifier was a bit disappointing. Hopefully this isn't a sign of things to come for Marantz.

 

[Dundas]

He has added several more complete teardowns:
https://www.youtube.com/channel/UCMeLTnjWzYeTRUm_FzysvPg/videos