Wow, I'll scratch that idea...
Perhaps a logic IR detector like PNA4611M00XD-ND from digikey.com would do the trick?
It will detect 36.7KHz(Easly Generated by the PIC) 940nm IR, and will provide logic signals providing it can detect the modulated IR from the TX.
Leads to another question, will the TX circuit handle those speeds? I'm thinking that the PWM signal will not allow the transistor to turn on and off fast enough to allow peak power from the TX IR LED