after doing some googling, I found out:
The control in and out are unmodulated IR codes inversed. 5V signal is Low, and 0V is High.
One COULD interface this with LIRC if they wanted to dig hard enough.
If you're having intermittent problems with IR, then maybe this is a path to look at.
it's not a serial port, so there will be external hardware involved.
I have a VSX1015TX with the same port, but the USBUIRT seems to work just fine for me. I don't think I'd get any benefit in a 'physical' connection.
One nice feature is that it's designed to also pass unknown signals.. so you could 'hide' a emitter on a device, and then 'hardwire' that device to the amp.http://wiredremotecontrol.blogspot.com/
is a good link on it.