Subwoofer pairing for Sonus Faber Elipsa SE

Currently have a 20+ year old M&K single VX-1250. It adds a very noticeable difference in fullness but looking upgrading

100% music, no HT

Full PS Audio BHK stack with 300 mono blocks

Already have GIK room treatments for 1st reflection and corner bass traps. My thought was to bring in a pair of matched subs.

Rel recommends a pair of S812's. @ $6k ish for a pair this isn't an option. The older 212 seems like it might actually be a better music only option but a pair isn't affordable. Seems like if I go the Rel route  it would have to be as a single. Maybe a used single G1?

Sumiko S.10 pair seems like a much more cost effective option. A pair is less than a single Rel. I read a lot how it's a variation of the Rel S5 with different cone material. Its unclear to me what the sound difference would be.

Last option is a pair of Syzygy 850. Beefer amp but only 10" compared to the Sumiko. Room correction is the interesting value here. Wondering how much value it adds.

I've ruled out SVS and the JL line is out of budget.  Feels like I have 3 real options

1) A single Rel, perhaps able to find a reference unit used 
2) Pair of Sumiko S.10
3) pair of Syzygy 850 for the room correction 

Thoughts? None of these can be auditioned within 1000 miles so looking to hear from anyone that has 1st hand experience with any of these

Thanks