I think where crosen is going with this is that IF the AVR takes the incoming TMDS data, decrypts it and then re encrypts it to send it to the sink, the new encrypted signal should be a good 5vpp data stream at the point it leaves the AVR, provided the incoming signal was ok and the AVR was working properly. This would indicate a restoration of a marginal signal from a cable box, say 4.8vpp back up to 5vpp.
If the above were true then when the cable box direct to the TV was good but bad when run thru the AVR it would indicate a problem with the AVR or the 2nd HDMI cable. The cumulative cable/connector db loss would be restored somewhat by the AVR if it is a restorer.

If, as many here have stated, the data from the cable box goes thru the AVR untouched (unrestored) it would complicate troubleshooting an HDMI problem.

Brent in post 8 said that sub 1k AVRs DO NOT rebuild signal level and indicated that more expensive units do. This would change what happens to HDMI inside AVRs and also change the troubleshooting of problems with HDMI based on model.

Is there a specification on an AVR that would tell how it handles HDMI?