Focal Aria 948

Honestly in this price range/speaker size you really need subs. An active crossover that allows for a highpass is really the key to good bass with domestic size/cost speakers. 
 

I have owned some of the products recommend in this thread and they all lack bass slam and extention. While Focal and Harman make great speakers they both roll the deep bass off for efficiency, or to keep the box small. Harman specifically seems to do this with both Revel and JBL these days. I own/have owned Revel,JBL,Focal and Klispch so speak from direct experience. 
 

Once you have a true full range system there is no going back. 

I currently have them running on my Antique Sound Lab Monoblocks Better than the SX 1250.  But still not the bass I would like.

Selecting an amp for those speakers if a deeper and tighter low end is what you seek is like chasing your tail. I had the Sopra II for a short while and paired them with Mac, Pass, and Coda and could not wring decent bass out of them despite a lot of positioning. At close to that price point, might I suggest the Dynaudio Contour 60...great mids and far deeper bass.

I use the Aria 948s with a Pass Labs Int 250 and Enleum 23R.  Plenty of bass. Speaker set up is key.  My room is 13’ wide x17’ deep and the speakers are 3’ off the front wall and 2.5’ off the side walls.  Play with toe in as others have said. 

Moved them around a little tonight.  1' from back wall, 30 inches from sidewall. Toe in slightly.  Sitting 12' back in a 12' by 18' room.  Better with this.  More tweaking maybe?