Mixing REL subs, great idea or terrible idea?


Short version:  Anyone have experience mixing and matching REL subs (T, S, R, etc...)?  If so, do you have any recommendations/warnings?  
Long version:  I have recently been integrating subs into my system (MacBook Pro > Allo USBridge signature > RME-ADI2 > Musical Fidelity A1008 hybrid integrated > Spatial Audio M4 turbo S) and have decided to use Rel subs for their musicality. I currently have a T7i parked in one corner but want to level out the room with another sub in the adjacent corner along the front wall. I love the T7i but keep coming across the occasional S/2 at a screaming deal but hesitate to buy as I’m not sure it will intégrate well with the T series (class AB amp on the T’s vs Class D, different chassis material, etc...). Not sure if these differences on paper would translate to any audible differences.  This is all further complicated by the sub needing to be white (for the WAF), and me being thrifty and only buying used (for the retirement). Anyone have any experience with this?  Bear in mind this will all be calibrated through DSP once the room is fully set up. The last sub and a new couch are the last items I am waiting on before starting room treatment and DSP. Thanks for chiming in!  Apologies as I am a noob at this. 
ultrabright
I read that the “i” series and the “sho” series are slight upgrades from their previous gens.

I’d definitely say go with the S series, especially if the price is right. I bought my S3 SHO from Magnolia. It was a floor model, no speakon cable, no box, and I paid $999. I bought my T9i from the same magnolia as an open box for $750...

@b_limo the frequency response curves I found of the T and Ti series are notably different. The Ti’s are rather flat in comparison, which apparently makes them easier to match to your existing loudspeakers. I haven’t found similar info for the S vs SHO’s but am interested to see if that series experienced a similar improvement.

I found an S2 for $750 but hesitated as I worried it wouldn’t match my T7i. I figured it would be more snappy with the class D power and sound out of synch with the T7i. Big mistake. It sold within minutes. Lesson learned.
For best results, google the 'sub crawl method' and then utilize it because it really works well and costs nothing. If the subs have room correction built in, you can run it afterward if you'd like. However, the most important steps are getting each sub optimally positioned in the room and in relation to your listening seat.

@noble100 I have a love/hate relationship with the crawl method. I now am also very tired of the Sneakers soundtrack haha. The T7i definitely comes to life in the corners of the room. It was really cool to hear the difference positioning makes.

I imagine that with the four 12” woofers between my Spatial Audios combined with a second sub (for a total of 6 drivers), I should have plenty of low end to fill my 12 x 14 x 9’ room, despite it opening up into a much larger (twice as wide and 12’ ceilings) space to my left. I’m surprised at how the addition of just one sub was able to pressurize the room as is. 
Get a miniDSP to give you find adjustments over both subs separately.

@erik_squires I will definitely look into one. Anyone have experience using mini DSP and Rel subs?  Any issues with the neutrik speakon cable?  I would like to keep my loudspeakers and subs running off of the same signal source if possible. 
I am not weighing in on one side or the other, but REL (and others) seem to generally advise against mixing different subs - essentially, the layperson’s explanation seems to be that because different models have different frequency responses, the 2 subs will never be reacting the same way to the identical signal they’re fed, resulting in potential distortion.

Seems to me you could adjust two different subs to integrate them together, but again, that just seems to be the view of REL.

I actually have both a t/zero and t/5i and do not like to run them together - I have not been successful doing that.
Unnecessary nervosa.

Get more subs, plug them in. Obsess about all the other stuff discussed here. 

Get matching subs to please your eyes.