Moving up in the REL line of subwoofers

Do the line array by added a second set on top of the existing. 

I second this. I have a REL S/510 six-pack line array, and it’s an amazing experience, with how it opens up the soundstage and adds realism. I started with just a pair, then a four-pack, and now the six-pack. I’d much rather have this (or even just the four-pack) than a pair of bigger subs like the 212.

Also the 212 cannot participate in a line array so that's the end of the line with them.

Thanks Guys,   so Dwette,  you had good luck with the four pack and preferred it over the 212?  

@ronkent Nice setup! Have you tried moving subs away from next to speakers? Often that makes a big difference. If they are well spaced in/around the room, then often more dimensionality is a welcome outcome. Refection on your reflections is my predilection.

Add a touch more gain? Adjusted the crossover?  Roast beaf and popovers? 

The 212se was replaced by the newer/upgraded 212sx in 2022 I think - do not know the technical differences and yes, the cost was quite higher...also do not know the technical differences with the new, just introduced 212...

@ronkent well if you have done pragmatic room coupling of the subwoofers I don't think you would be having upgradeitis