Check the following link, and about half-way down on the scroll bar there are several closeups of the cooling tunnel showing the attachment of output devices w/heatsink compound (appears to be two channels of the 510/710), a downward overall view of the tunnel, and an end view looking into the tunnel from the exhaust end with the fan at the intake end. This review appears to be pretty descriptive, so I wish I could read French!
Anyone here capable of translating?
Anthem's tunnel appears to be a four-sided enclosed extrusion with additional radiating surfaces protruding into the interior. As such, all
surfaces of the tunnel become a "sinking" device, even the exterior surfaces inside the chassis. Overall, this looks like a fair amount of radiating area for heat dissipation, with the added benefit of a number of interior "fins" that draw the heat away from the output devices into
the tunnel. If the fan isn't running, this performs similarly to the "vents and heatsinks" arrangement you mention. However, once the temperature hits a certain level, the fan will kick in. With the fan forcing air through the tunnel and exhausting outside
the chassis, heat radiating from the exterior surfaces to the chassis' interior is minimized (which should help adjacent components remain cool...and certainly cooler than passive sinking inside the chassis where the only escape route is via top-venting). This method of cooling is very similar (if not identical) to that employed by Marantz in their 510M amps back in the 70's, and in over 25 years of use I never had a problem with over-heating...ever.
I can also tell you this: compared to my replaced Onkyo 705 (w/interior chassis sinking and top-venting), I can push the snot out of my 310 and the top of the chassis above the tunnel never becomes more than barely warm...regardless of fan speed. With the Onkyo, I could nearly heat the room (OK...a slight exaggeration...but Onkyo was known as a hot-running AVR).
Bottom line: I really wouldn't worry about the cooling tunnel. As a matter of fact...I'd prefer it.
Here's the link: http://www.hdfever.fr/2014/02/07/tes...510-et-mrx710/