Personally I couldn't recommend the Pioneer / Radius combo highly enough (presuming the balance of sound is broadly similar to my VSX-2021, although I appreciate that the LX75 is a significant step up in quality). I do concede that many recommend Yamaha receivers as a good match with most Monitor Audio speakers.
However, I do agree with BigBoss that you should demo; and the precise choice of WHICH Radius speakers you demo will have a impact on the match. I personally find the Pioneer / Radius combo to be fast and precise with pin-sharp steering effects; grin-inducingly so! The midrange however has a beautifully fluid lush quality about it, although this quality is stronger and more pronounced with the R270HD floorstanders than the R90HD's if you're using these as your main left & right channels.
I found that the slightly stodgy bass with the Pioneer receiver is tightened up nicely by crossing over to the R370HD sub at 80hz, so the sub's amp not the receiver's amp deals with the bass anyway.
As much as demos are necessary, they do have their limitations that you need to be aware of. I found that the tweeters mellowed considerably after a couple of months use, so I'd recommend asking how much use any demo models have had prior to you hearing them. Also, I found playing music was best with the setting 'Extended Stereo' which plays a straightforward stereo signal through all available speakers, but using the Pioneer AV receiver control app to weight the balance slightly toward the front speakers.
For movies I prefer the 'optimum' setting best which raises dialogue to the fore and reduces the 'get the remote quick because my ears are about to explode' reactions to sudden changes in dynamic range to movie soundtracks.
These details may seem pedantic, but they make a huge difference to the type and feel of the sound, so if you had it set up wrong when you listen to the demo, it could wrongly influence your view of the quality of the product you listen to.
Hopefully any decent dealer would be able to advise you on the best settings for your chosen shortlist of receivers, but it's worth taking a little time experimenting with the settings at the dealers to see what suits your personal taste best.
I found the match of Pioneer / Radius so much better than I expected (especially for music when played in Extended Stereo) that I've now ditched my original plan of having a separate Naim Unitilite for stereo duties.
Finally, I'd take your room shape and size into account. If your room is small to medium, the Radius will be excellent. If your room is large, I'd consider trying out the Monitor Audio RX silver range as an alternative.
Happy demos, and let us know how you get on!