So it seems common IR equipment (xantech, proficient, channelvision) operate at 12V, including emitters, blasters, hubs, and eyes. I'm using a combination of xantech and proficient IR hubs.

However, my NEC PX-50XR5 display uses 5V (wtf?) on the IR remote in/out ports.

How the heck can I cleanly feed IR signals to the display without sticking on an IR emitter? Or have the display relay the IR signals?

In other words, how do I convert a 12V IR to 5V IR and vice versa?

A couple of resistors will knock it down to 5V (google voltage divider), but it's not so easy going from 5V back up to 12V.