Chris, you're partly correct and partly incorrect. The PR-81 isn't stereo, it's mono but it makes non-standard use of the 3 pin output.
The PR-81 uses an XLR connector but not to carry a balanced signal. Pin 1 is ground. Pin 2 is an unbalanced audio out and Pin 3 is an unbalanced headphone level out. How this is utilized depends on the output cable that's used and any adapters connected to that cable. If you use an AKG cable that has a mini jack, you can get a two-channel mono headphone signal in both sides of the headphones. Again, it's not stereo, it just appears in both left and right with the same signal. You shouldn't be using this output to record from though. It's too hot for the recorder input and the headphone amp needs a minimum amount of impedence from headphones or it can burn out.
The meter I'm talking about is a simple electrical meter available for $10 to $200 that can check the continuity between the female sockets of the XLR adapter and its RCA output. Maybe a friend has one?

interesting... I sit corrected

The AKG receiver comes with a mini jack output as well as a XLR. The male part (I don't know what you call it) is in the stereo shape and when I plug it into my small camcorder, you can hear the mic in both sides of the headphones. My mono shotgun mike only shows up in one channel of my headphones.

It's no big deal. I've decided to use two cameras: one in VCR mode with the lipstick camera and another in camcorder mode with the wireless lav. It's probably better to record that audio separately anyway... plus, I'll have more footage to work with.

That must be a new cable that they didn't have when I got my two systems. It probably uses the Pin 2 output and splits it to both channels of a stereo mini. It's still two channel mono, but it's the proper way to get the signal into a stereo input.
I'd still like to know why the XLR to RCA converter didn't work though.