UPDATE: Went to the store today and picked up an MRF-350. Swapped out the new RFX-250 with my existing antenna module and everything is working just fine.

Range appears to have improved (over 60 feet) with all remotes (pre-2006 MX-850 works, along with 2004 MX-3000) and the response is noticeably better. I didn't actually do a count, but after fiddling with numerous button presses, I would guess that less than 1% of commands are missed by the RF base station. (About the same as older setup).

One other thing... Is a MRF-300 basically identical to a MRF-350 in circuitry? Are there any advantages to swapping out the base stations? Or, with the RFX-250 attached to the 300, will it function exactly the same way?

If there's a difference, I guess I'll eventually get around to swapping them out. Otherwise, if it aint broke...

Thank you all again for your help.