I made the switch to Direct TV.
(...)
my ReplayTV 4504 and how long it takes to change channels.

As much as I want to support DNNA, and as good as the Replay TV units are, I must suggest that you consider one of the integrated two-tuner DirectTivo units. They're dirt cheap, can record or view two channels at the same time, and don't have to do any IR blasting to get the job done.

Truth is that the only reason I'm using DirecTivo over ReplayTV right now is the integrated satellite receiving. I wish the ReplayTV units had that feature.