Different brand/model Sub(s) integration

Servos on subs are only necessary when you are asking drivers to do things they do not ordinarily do.  It is a sign of poor or undersized drivers. Large well designed subwoofer drivers have no problem maintaining distortion levels below 0.5%. You run into higher distortion levels when you start asking drivers to take long excursions. If a driver is taking excursions greater than 1/2 X max than it is too small for the job. You can either use larger drivers or multiple drivers. 

I've not heard sub that sounds as clean and crisp as my Rythmik servo sub. So if that is wrong I am very happy with it being wrong!

@mijostyn I want to keep everything as analog as I can, so DSP inline with everything else is not an option for me. I thought you were talking to make a crossover network among the subs.

Thank you for the suggestion 

Sell the Rel?...Thats a really stupid idea!...You own the best selling subwoofer in Rels lineup and it is  for a reason.Outside the reference #25 and the G2 you are there.I had the same issue with the same sub.I tweeked my room some and fix it a little...but when i bought another S510 thats when my system came alive..Yea you can go with another inferior subwoofer but at the end of the day thats exactly what you have.I would never take advise from someone who has no first hand experience with the product..cheers and happy tunes

@missioncoonery  do you want it for free 🤣 no worries I will not sell the REL... 😂. I have a room with 3 G1 MK II, and another room with 4 #25s in my actual home. 

In my house in the USA 2 510s will be tight that is why I was thinking something smaller and different response with the hope to help the room mode.

I am getting another 510.