I also augment the bass on my Cubes, and whatever other speakers I'm using, with a pair of REL Carbon Special subs. Before that I used REL S/510's which were also excellent. I know some people shudder with the mention of subs but once I tried a pair of RELs I can't really go without. I barely have the subs turned up on the gain dial to probably around 20% and tend to cross them over around 50-60 hz. They really just add some punch and weight and depth. When I sold my S/510's, the guy who purchased them had eschewed subs forever. He had a pair of high end Gryphon standmount speakers that got great bass. When he hooked the subs up he wrote to me and said he couldn't believe how much better and deeper the sound was. I don't want to change the topic of the thread, but my point is don't be afraid of trying some subs with single drivers to help get the extension you want. That being said, I've listened to my Cube's without subs and the bass is excellent. It doesn't rattle the windows but it is full, detailed and fast. In the right room you probably wouldn't need a sub for 95% of music listening unless you really want to feel the bass.
As far as amps go, I've always heard that the Cubes prefer amps that have little to no feedback and have a low damping factor. I remember reading that's because the magnet structure of the driver is so strong and the driver is already "damped" or heavily controlled by the magnets. So an amp with a high damping factor can over control the drive and make it sound dry and dull. I've read reviews where the reviewers have preferred lower wattage, low damped amps vs higher powered amps. I've used probably 10+ amps with my Cubes and I have also found that to be true. I currently have 3 main amps I rotate: Line Magnetic LM845 Premium, LTA ZOTL40 Ref+, Coda S5.5. All sound different but excellent with the Cubes. I've even used a 1.5wpc 45 tube amp and they sounded excellent. I've used everything from GanFet class D, Class A, Class AB, tubes, 300b, 45, 845, EL34, KT88, etc... and all sound great. But I do generally recommend lower power, lower damped amps with little or no negative feedback.

