If you like your ATC mains and have the space in your room, I think I have a good solution for you.
It's called a distributed bass array system and it provides state of the art bass response in virtually any room and integrates seamlessly with any speakers. It basically consists of 4 subs strategically placed in the room that delivers exceptionally good bass throughout the entire room, not just at a designated 'sweet spot.
These dba systems can be purchased as complete kits (4 rather small 2.5'h x2'w x1'd unamplified subs with a 1K watt amp with equalizer and crossover) such as the Audio Kinesis Swarm and DEBRA systems for about $3K or you can build your own custom dba using your choice of subs. Here's a link to a review of the Swarm system by The Absolute Sound:
http://www.theabsolutesound.com/articles/audiokinesis-swarm-subwoofer-system/
I have large Magnepan panel loudspeakers which are notoriously difficult speakers to integrate with subs. I bought the Audio Kinesis DEBRA complete kit( almost identical to the Swarm) a few years ago and I'm thrilled with it. It's given my system seamlessly integrated bass down to 20 Hz +/- 3dB that's capable of reproducing accurate, natural and life-like bass whether the bass content is deep and powerful or fast and taut.
I'm almost certain a dba would work equally well with your speakers and room. Audio Kinesis also offers a 30-Day in-home trial period .on the Swarm and DEBRA.
I have no connections of any kind with Audio Kinesis, I'm just a very satisfied customer.
Good luck,
Tim