The response for REL regarding subwoofers

Horn loaded subs at 95+% sensitivity. Maybe a pair of 12" per enclosure, two enclosures. They are huge but that's what I use to run with Western Electric, VOTT or any Klipsch. Back then we didn't have to many box subs. There ones like REL but passive, the passive radiator was on the bottom too. It wasn't in an enclosed slot. 60-70s not too many manufactures made subs. You had to make them. Jensen Imperials Subs are a ton of fun. With 60-100 watt.. Your bumpin' pretty good.

https://www.decware.com/ImperialSO.htm

I had one and my buddy had one. When we had a party there was one at either end of the packing shed and a pair of Jensen Imperials. 

2 20 watt MACs and 30 watt Mac Kit for my sub and speakers and 60 watt MC60 for his. Would fill the whole joint right up.. 1969-72

That's what you need OP a big fat one dead center of those KHorns :-)

Regards

In 2001, I was using a Velodyne FSR18 with my Khorns and had no issues, mind you the neighbors did....

I’m using a GSG Devastator with my Altec A5 setup. It’s a 21” driver in a semi horn style enclosure. It’s powered by a Behringer 3000 dsp amp and I’m actually using the sub amp at about 75% on the gain and 35% on my Preamp volume and they blend well.  It is a huge cabinet though

Sensitivity is irrelevant. Volume level is what you need to match with subs, period. Clearly REL is capable of high volume levels. Cornerhorns achieve high volume with less power, but you listen to volume not power. Think about it. 

The wife is always playing with the volume control on her system if they weren’t matched like a La Scala with normal subs, she wouldn’t shut up. Having to get up and turn the volume up or down on 3 plate amps when there is a main speaker volume change.

I went from 84-5% Dayton Ultimax to 90% sub drivers listed below and I run 1/4 the power and reach lower than with the most 12" drivers. 4 in a 12cf column with 1 15" passive radiator. hit 120db and 16hz. It’s one of the best sounding columns I’ve ever heard for the money. I’m using 8" MB drivers and GRs OB servo on mine now, that Servo wouldn’t work either I don’t think, I’d have to look.

I use Behringer for bass duty NU12000. I keep 3 here 27 lbs brute strength class D pro amps. Well over 2500 watts per channel @ 8, 3500 @ 4, 4500 @ 2 ohms.

These 10" might keep up better let’s say.. :-) It’s my secrete weapon. Works very well in a 1cf sealed box to a 3cf with 2 12" radiators @ 18hz. Serious driver. Of course they went up 60% in the last year..