Can you please clarify your situation. Are you going to be using your Maggies for HT or just for Stereo? Are you planning on keeping the Yamaha for HT? Do you have a sub now?
Something to research, I believe with some processors if you don't define a sub to the system and define your fronts as large, they will send all low frequency signals including the LFE channel to the fronts. Is that true with the Yamaha? If so you might be able to run the Maggies as large full range speakers and use the cross over in a sub to accomplish your purposes while avoiding the sub processing in direct stereo mode.
While I love my RR2150, I can't see much use for it in a HT room (others feel free to correct me). If full separates are out of the question. You may want to consider using a separate two channel power amp (there are plenty of these available used) to drive the Maggies. I am fairly sure the Yamaha can run a preamp out to a separate amp. Alternatively, you might want to consider a separate 5 or 7 channel amp and forget the Yamaha's internal amps altogether.
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Living Room 24x18 open 1/2 flight up to a raised dining room/hall 24x12
Outlaw 976 pre-pro running 5.1 system
Outlaw 750 for Artison Masterpiece LCR and 2 NHT SuperZeros rears
Velodyne Servo FX-1200
LG OLED65C8PUA via HDMI2 to/from 976 HDMI ARC
Roku Ultra
Samsung BD-D5500 BluRay
Amazon FireStick 4K to 976 Aux HDMI input for Amazon Music Ultra