Question for those who use REL subs with Wilson speakers

Sorry, can't offer any opinion, just a couple of comments.
Do you use corner bass traps? If not, you might get more effectiveness with them.
Have you tried stacking the 2 subs that you already have to get a sense of what it might sound like having them stacked? Try doing to both sides of the room.
Just curious how big your room is, and what amp your using. How are you connecting the subs (amp-speaker cables, xover, preamp).

Hi golfnutz, thanks for the questions and suggestions. I have not tried stacking the subs.  My room is a boy 15x 20. However there are 2 doorway sized openings in the corners of the right side and one on the left wall about 3/4 of the way toward the wall behind listening seat. I use Stillpoints Apertures. Concrete floor with carpet and pad. Using Musical Fidelity Nuvista 800 amp, connecting RELs via Bassline Blue cables to amp speaker binding posts as recommended by REL. I consulted extensively with their customer support techs during setup and tuning.

Website says the Apertures go down to 40HZ. I would be inclined to think bass traps in the corners would be more effective. Maybe talk to REL and see what they suggest (they could tell you adding more subs will overload the room, or could be of no benefit). Might want to consult with one of the acoustic companies about bass traps to see if they can offer any advise.
Anyway, good luck, sounds like you have a really nice system.

Great suggestions, and thanks!

Just one more thing Arsh, I was looking at the amp tests at Stereophile and it was suggested to JA not to bother testing the amp down to 2ohms as Musical Fidelity says using speakers under 4ohms for prolonged period of time isn't recommended.

Not only does the impedance drop below 4 ohms for most of the lowermidrange and upper bass, with a minimum value of 2 ohms at 86Hz, but there is also an amplifier-unfriendly combination of 3 ohms and –43° phase angle at 61Hz.

From what I read about the REL and the way you have them connected, there is no xover, and both the REL subs and Sasha woofers are active and operating independently (if this is incorrect please comment because I would like to know myself).

I'm just wondering if using a different amp will give you more bass/mid bass/lower midrange instead of relying on additional subs from what you have. I have a feeling a different amp will help you more than additional subs will. I also think no matter what amp you have, the subs you have already will help regardless, especially for the 2ohms at 86HZ dip.

Might be worth something to pursue if you could borrow an amp that doesn't have issues going down to 2ohms (friend or dealer). I think if your willing to pay for shipping you could even try a Pass Labs from Reno Hifi (I'm not recommending Pass Labs, just as a way to test the theory).