Someone more knowledgeable will correct me if I'm wrong, but disabling the MD/Orbitor on the core will only affect your ability to VIEW media on the core. The tuners are managed by MythTV or VDR (whichever you chose to set up when you installed LinuxMCE) and will run as background services. I'm more knowledgable about Myth, as that's my present "production" environment at home (I'm testing and doing some infrastructure proof-of-concepts on LMCE right now, so it's not "prod" yet).
My MythTV backend (which would be a LMCE core) runs headless, and has two dual-tuner PVR-1600's in it, and it can use the two PVR-150's that are installed in a slave backend/front-end in the family room. Myth is really great for running a distributed system, and you can run any combination of backends and front ends as your situation may require. Since LMCE leverages Myth, you inherit those capabilities.
Hope that helps!