Moving up in the REL line of subwoofers

I almost bought a used 212SE from TMR for around $2000 ...but it’s now gone...have seen there the 212sx close to $3000…

What is the difference between an 'SE" and a 'SX"? besides cost, if any...Thanx!

Do the line array by added a second set on top of the existing.  There is a pair for sale at a reasonable price in the Atlanta area at the moment.

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?