I thought i'd post this in case it helps anyone out. I'm on my 2nd Monoprice 4x2 switch (now at rev3.0) after having issues with the rev2.5 version, and i've still been having the 2ch PCM-only audio output issues to my AVR. Here's the relevant parts of my setup:
1) Scientific Atlanta 8300HD PVR
2) Oppo DV981-HD DVD Player
3) Toshiba HD-35 HD-DVD Player
4) Panasonic DMP-BD30 Blu-ray Player
A) Samsung LN22A450 TV
B) Yamaha RX-V1800 receiver to Panasonix PT-AX100U Projector
....all switched through the Monoprice 4x2 switch, controlled by a Harmony 880 remote.
I spent a lot of time troubleshooting cables, unplugging the tv, switching inputs/outputs to try and re-'handshake' etc, but the last thing i want to be doing is unplugging the tv from the switch or anything else like that to get things to 'work', or telling my wife that's what she needs to do every time she wants to watch anything on the big screen
I found that after setting the desired activity e.g. watching Blu-ray (input 4) via the receiver/projector (output B) with the HDMI switch set to the correct input/output (4B) as normal, i would then press the 'A' button (output to tv) at least once, ensuring it was not on the input i was wanting to use i.e. '4', and then press the 'B' button to cycle away and then back to '4B', and 'voila' the receiver is getting the correct audio. This seems to work with the other devices also
Now, i know that extra 2 or more button pushes on the switch is a pain, but i programmed each activity on my harmony remote to add these 2 infra-red commands at the end of each activity set-up, and so far it seems to work.
So, one button press on the remote, and everything appears to be working fine. No unplugging cables or anything like that. We'll see what real world testing brings i.e. turning everything on from 'off', as opposed to just switching back and forth between activities like i was doing this morning....
Worst case scenario if you don't have a universal remote is a few extra button pushes on the front of the HDMI switch.
Not saying it'll work for everyone, but give it a try.