Hello stickman 451,
Are you sure you really want to move on from your Magnepan 20.7s? I believe you'll likely regret it for numerous reasons that will likely become painfully obvious once you switch to any other speaker options anywhere near their price point. Yes your room is large at 21.5'x30' but given your high quality system and speaker components, I suggest you explore methods of optimizing your current system prior to seriously considering making any possibly unnecessary and costly changes.
I'm basing my opinion on you already owning all the required excellent component parts to achieve near state of the art full range sound quality performance in your room and my personal experience achieving similar full range results with less expensive system component parts and in a smaller 16'x23' room. I utilize Magnepan 3.7i main speakers in combination with a 4-sub distributed bass array (DBA) system very similar to the Audio Kinesis Swarm system reviewed by The Absolute Sound in the link below:
https://www.theabsolutesound.com/articles/audiokinesis-swarm-subwoofer-system/ I can attest to this review being a very accurate description of the very high quality bass and seamless bass integration with your 20.7 main speakers you can expect, even in your larger room. Because you already own a pair of very high quality REL G-2 subs, however, I know you have other options for attaining excellent supplemental bass performance in your room.
If you're mainly concerned with performance results at a single dedicated listening seat, I believe you can do so by just optimally positioning your two G-2 subs and 20.7 main speakers separately in relation to your listening seat. I could describe exactly how to do this or you could request your local REL and/or Magnepan dealer come to your home and do it for you.
If you prefer great bass results throughout your entire room, I'm as certain as I can be that you can do so by either utilizing the 4-sub AK Swarm DBA system or creating your own custom 4-sub DBA system. This could take the form of adding two more G-2 subs and optimally positioning and configuring them. But I believe it could also take the form of adding two more smaller REL subs, such as the 7i or 9i units, and achieve very similar results.
Another option is the 6-sub distributed line array bass system suggested earlier by mijostyn, either with your 20.7s or his suggested Sound Labs 845s. I agree with him that having 6 subs lined up along your front wall is the ultimate bass system in terms of volume and dynamics, however, you or your domestic partner may not accept the room décor statement of 6 subs lined up along your living or family room wall. But if you have the freedom, I think it's the only bass system that could equal the 4-sub DBA's bass quality and exceed its bass SPL levels.
As to your thread topic, though, Magnepans have been my favorite choice for main speakers but, if I had to pick others, I'd probably either choose Sound Labs, Tidal, Vivid or Magico.
Best wishes,
Tim