I have 2 remotes. MX-900 and MX-980. I only tried the MX-900. I did try different emitters with same bad result.

serial number of MRF-250 is either K042406 or 097447 (this is what was on the sticker)

serial on mx-900 is B121007 0113306

and if someone could tell me what "buffered" means, that would be great. Always like learning new things