A sub? Loads of bass here pal, I reckon I could give my old 3090's a fair fight.
I had mk2 Kans and when set-up tight against a solid wall, on Kan stands, with a Naim Nap 250 and modified pre-amp/CDP I could get some very good punch from Kans, but depth was always missing. I added a good quality sub (Rel Strata 5) and it made a HUGE improvement.
You'll get better bass than a lot of three way floor standers with a sub, for a number of reasons - The Allison Effect, the fact that it's active and has adjustable phase and level, the fact that the driver is designed to produce sub-bass and has a very high xmax. The fact that the box is as solid as a rock and away from the midbass and tweeter and the fact that you can move the sub to suite your room acoustics.
Some people think that a sub wont keep up with their speakers but this is a myth. The Bk sub that I linked is sealed with a box q of 0.5. A box q of 0.5 will be very fast and accurate. Some subs are designed for av use and have a high q and as a result, slow bass.