IMO, the MR100 may work OK as an IR receiver plugged into the new receiver's IR input jack. You'll have to try it & see
Pioneer's older multiroom interface was not standardized for standard conventional IR devices,. such as Xantech, because of a non-standard connection inferface with a different ground scheme. I know this from personal experience
the miniplug & jack pin-out was different. In fact, Xantech had a special interface module that could be used with Pioneer's MR & I even tried that but could not ever get it to work with a VSX-49txi.
that said, the MR100 itself was a normal IR receiver so may work OK with std IR connection even if it's a "stereo" jack. if it doesn't, then you have all sorts of options - replace the MR100 with one of Xantech's IR receivers & transmitters, Niles Audio, Russound, or use a programmable remote with RF-to-IR transceivers, such as URC.
For plain jane IR, Xantech is hard to beat.
but give the MR100 a try, it may just work just fine. it's nothing special being a normal IR receiver, but the catch is whether its miniplug connection will be compatible with the IR jack on the 1122. I know stereo 3.5mm miniplugs will work just fine even though IR only needs a monoplug.