H25 HDMI output Strength

[harshness]

Right. I'm not sure how this config can handle multiple receivers which may not all be configured the same. It seems likely that the signal is being rejected at the DCOM, as you say because it can't "come to terms" with the multiple devices. Maybe all the receivers are set to native "off" except the H25s...... My suggestion is that the OP makes sure all the receivers are native off and set to the same output resolution.

I'm guessing that it needs to negotiate the same parameters from each and every device and it does that through EDID. If the H25 somehow isn't up to it, it takes its marbles and goes home.

Here's a commentary from the HDMI website regarding troubleshooting:

http://www.hdmi.org/installers/interoperability.aspx