Speaker size and room interaction

The T5 hits amazingly hard. Excellent little sub for sure! 

I'll be curious how you deal with sub-to-sub interference, etc. I would like to get another sub, but I've heard (a) that it should be identical and (b) that one can create additional problems by having them interact.

If you’re using the bigger subs in the room with the Fritz speakers, I’m not surprised you experienced overwhelming bass. Somewhat cube shaped with sheetrock? Wood floors?
I use a S3 in a 40x24 basement space with no boom issues. Enjoy the T5(s).

I wasusing the S3 with Totem Arros.  Horrible choice.  With just one click on the volume, it would go from too soft to too loud.

Don’t get me wrong, the S3 is awesome and superior to the t5i but not in my room.  I bought the S3 new from magnolia for $999 btw!
Another really strange thing is how well the t5i integrates.  Like I said, I just plopped it down and that was it.  And something else somewhat strange is that it sounds good in phase and 180 out of phase, both.  
This is my first downward only firing sub and I’m wondering if I prefer them.  
Anyhow, the T5i has thoroughly impressed me.  For a little 8” sealed sub, it is just fantastic.  At the $275 I paid for it, its probably the best bargain in my system.

Hilde, I would think that using multiple of the same subs is best but the swarm guys say it doesn’t matter.  I think the main thing is having multiple sources of bass output in differing locations simply to create less dips but I still don’t see why using 4 of the same wouldn’t be best.  Which Rel do you have?  I’ll keep an eye out for another one...
Anyhow, I am super stoked with my set-up.  It’s reaching the point where it is in the top best sounding systems I’ve heard and its mine!

I have the REL 328. TMR and REL themselves advised I get another one of the same make *even over another REL.* Then, there are folks here. This is the hobby-of-directly-contrary-advice and the you-gotta-just-try-it. A minefield for expensive mistakes.