A long time ago, I had the Primare A20 MKII (your amp's ancestor) with Dynaudio 52 monitors.
I used the REL Strata III sub via high level outputs; it blended very well.
I don't think you need to spend big bucks to get the benefit you're looking for. Certainly closer to $500 than $1000, put it that way. If I was buying again, I would think about a kit like this:
http://www.madisoundspeakerstore.com/subwoofer-speaker-kits/sb-acoustics-12-powered-subwoofer-kit/
I used the REL Strata III sub via high level outputs; it blended very well.
I don't think you need to spend big bucks to get the benefit you're looking for. Certainly closer to $500 than $1000, put it that way. If I was buying again, I would think about a kit like this:
http://www.madisoundspeakerstore.com/subwoofer-speaker-kits/sb-acoustics-12-powered-subwoofer-kit/