Subwoofer matching


I was all set to pull the trigger on a pair of REL subwoofers.  These would be used with my Avangard Duo’s and Pass Labs XA 60.8 monoblocks.  My main music is Rock, Jazz and Blues.  I have been given advice by a few people now saying the 107 efficiency of the Duo’s will make it very difficult to find a matching paint odd subwoofers.  Feed back I have been given is “... it will take a powerful subwoofer to be able to match the output levels of your speakers“ and “The only REL model that may work for this application will be the 212/SE, which has a very powerful amplifier that will allow it to blend well with your speakers.”  A pair of REL 212/SE is a budget breaker for me.  I am in not position to judge if the advice is correct or not.  Does anyone have experience negating a pair of subwoofers to a highly efficient speaker?
chilli42
Chilli, Any subwoofer that can match the volume you like to listen at will be fine. Most of us rarely listen over 95 dB and any pair of 12" subwoofers will do that easily. They all have adjustable gain. You just adjust it to match the output of your main speakers. It will require more power to reach the same volume but all the decent subwoofers are equipped to handle that. The 4 10" drivers you get with the swarm system will also do just fine.
So, unless you listen at 115 dB any decent subwoofer can be made to match your system. You are right to start minimally with two. 
Aside from matching the listening volumes, in my experience the bigger issue is matching the ‘speed’ of the subwoofer driver(s) with your horn system. The suggestion of using multiple small driver subwoofers is much better than using one or two large driver units.
What deficiencies are you trying to address?You don't say whether the subs are meant to compliment the AG subs or replace them. If it is the latter, bear in mind this bit of info, as per Jim Smith years ago, that the AG Duo subs, (the sub 225 in my case), have "meaningful" output up to 500 hz. You could end up with a hollow midrange if your intent is to simply jettison the factory subs. I have no idea what "...negating a pair of subwoofers..." means.

I would do a little more investigating and proceed (or not) with caution.
I have 99db efficient horn speakers and use 2 RELs (bought used in mint shape for around 200 bucks each...a 10" and an 8") with 'em, and have never sensed a lack of "speed." They have input level controls along with phase and frequency adjustment...works swimmingly.
The quoted words of caution are from REL customer service.  My I am suspicious but they recommended two of the biggest most expensive subwoofers they sell.  The REL recommendation was seconded by a couple of friends.  I am also considering SVS subwoofer.  They did not seem to think that their subwoofer would have a problem keeping up with the AG Duo’s.

The reason I am not keen to buy AG subs is that I don’t want to have flexibility issues later if I migrate to a different main speakers.