Hi,
I'm using a HAVA Titanium to access my set top box. I set it up following their guide and it works perfect from the PC MCE. The problem is, when I access it from the DSM-750 extender it doesn't accept the IR remote commands. I can watch the channel that is actually playing on the TV tuner. I can see the guide, but when I select any of the channels in the guide or type a number it doesn't go to the selected channel, the guide goes back to the original one. Again works perfectly from the PC even with an MCE remote.
Just in case let me inform you that the HAVA uses its own IR blaster and the MCE remote is only necessary to trick Windows Vista MCE. It doesn't really matter how you setup the IR remote on the MCE, HAVA uses its own method to change the channels.
Another comment, if I disconnect the MCE IR remote and setup the TV Tuner as an analog cable box, I'm able to change the channels from both ends, PC and extender, but only local listings (channels under 100 although I can see the whole guide). In this case the funcionality of the remote for live TV is very limited.