I spoke with Comcast at length again. They claim the problem is with Denon's HDCP capabilities. They have only 1 brand (Motorola) and 1 model HD DVR (DCT6412 III), at least in my region (Philadelphia)

I spoke with two local high-end shops that sell the 4306. Both have had problems, the one shop I spoke with for about 30 min and they've had same problem with (2) 4306's and a 4806. 2 customers were using Comcast's HD DVR, 1 was using Direct TV. Their research pointed to a problem with the DENONs and they said they were told a firmware update would be out in a few months. Their solution is to go back to componet and optical inputs for the DVR

I got ahold of DENON/Marantz tech support. They claim they'd had several customers call in with same problem, all using either the Motorola or Scientific Atlanta DVR's. DENON's position is they are 100% HDCP/HDMI compliant and in their tests, the other manuf's equipment was the problem. They are doing nothing to correct any problems and they suggest just waiting until an update comes out from Comcast. They tech said a SA update is due in March for known HDCP issues, but no word on Motorola.

I've got a family member at Motorola tracking down a contact person there to follow-up on the problems and a date for a possible solution.

What I don't understand is, if the DVR works fine with the TV, why wouldn't the HDCP issue be in the DENON...the picture only disappears when the DENON is in the loop so wouldn't this be the most likely cause of the problem? I have a rought idea of how the HDCP works, but if there's an issue with the DVR's HDCP, wouldn't I also have display issues when connected to TV via HDMI?

Thanks again