I've been trolling though the XM Fan and MP3 Car Audio forums after seeing this thread. I was under the impression that XM Direct can be controlled and interogated with the same serial codes as the XM PCR by sending it 3 serial commands prior to launching the PCR software. At that point it behaves like a PCR.

XM Direct has analog outs as you said but I believe it's possible to add digital outs (Coax or Toslink) for about $35.

Please correct me if I'm wrong. I was actually interested enough with the concept to order in a XMD tuner.