Sorry about the trouble.
Some random, not well thought out ideas for isolating the problem:
> Verify all devices (e.g. TV) are running the latest firmware.
> Is it possible to relocate the 8642 set top box to the room with the TV and connect the STB directly to the TV using only a short HDMI cable?
Was the (reversed) Redmere ever connected to the 8642 set top box? Could that have damaged some of the STB HDMI output signals...
> If you have another source device with an HDMI output (i.e. a Blu-ray player), try that remotely using the Atlona transmitter/receiver.
> Try powering up equipment in different sequences. For example, power up the TV, then power up the 8642 set top box, then power up the Atlona transmitter/receiver. OR, power up the Atlona tx/rx, then power up the TV, then power up the STB.
> Power up everything and then redo the STB HD setup wizard, if any.
> Atlona tech support probably would be well able to help troubleshoot.
Hope this helps.