Here is what I do at home. I have a dish network pvr 522. The primary IR output is hooked up to my core in the living room. The secondary RF output is hooked up to the MD in the family room. Now, If I am recording something on tuner1 on the core, and I go to watch LiveTV on the core, it automatically calls up the tuner on the MD. Also, I have a key prgrammed in mythtv to switch inputs on my remotes. This will automatically draw from whatever card is not in use.
If my daughter is watching PBS in the family room, and I tried this this weekend, by using the "Switch Inputs" fuction on the LMCE menu, I can view her TV on the core. After seeing this happen, it turned off her show, and then automatically changed the channels on the core tuner, to let her continue watching her show.
This also works using the media map feature from the orbiter. So it does work, its just how you go about selecting what to watch on said MD's orbiter, or on a remote orbiter.
The key for switching inputs/cards on mythtv that I use is the "Y" key. It will cycle through all cards attached to mythtv. I have 2 pvr150's and 2 air2pc HD tuners (OTA) using the "Y" key or the "Swtich Inputs" option in the LMCE menu, it cycles through all 4 cards, provided that they are not being used to record something at that time.
You can change your keys using mythweb(http://dcerouter/mythweb/
) to use whatever you like, and then map these keys using xmodmap to a remote key. My howto for mapping keys is here http://wiki.linuxmce.org/index.php/Using_the_Gyration_Remote_GYR3101US_%28Non-Fiire_Chief%29
in the wiki, and it works well, without installing any additional software.
I hope this helps. And I look forward to your mce_usb2 howto, so that I can get my mce blaster working on the MD.
Best of Luck.