Sounds like you've tried just about everything, but have you tried using the original remotes with the IR extender?

If the original remotes fail, it really only leaves 2 possibilities:

The IR extender is modifying the codes.
Despite hours of trying, you haven't found the right place to stick the emitters onto the devices.


Might be worth trying a simple IR extender, rather than the fancy one you're using. I bought a no-name extender on eBay UK for 10GBP (15USD). The receiver looks like a computer mouse, if you want to search eBay USA.
This device works perfectly with my TSU9600 and Arcam AV amp, which is very fussy about aligning the remote, as the IR receiver is mounted deep behind the fascia.

Some European cable/satellite/TV boxes have the facility to use a "magic eye". This is a device that connects in-line with the RF (antenna) output to remote TVs, receiving the IR signals and passing them back to the box via the coaxial cable.
Do US boxes have this facility?
I couldn't find where to stick the emitter onto my Sky HD satellite PVR, so I'm using a "magic eye" - works perfectly.