Upgrade from ADS L1230

Hello, I am the lucky owner of a pair of ADS L1230.

I like the amplitude of the sound-stage and the tone is very balance with a sweet, soft and well defined mid-high.
What I am missing is definition on the low-end. I feel like the bass is not as punchy as I would like and in general I perceive some sort of sluggishness at the lowest frequencies. 

I would like to upgrade to a pair of speakers that would give me the same sound-stage and pleasant mid-high and at the same time better performance on the low-end. I was thinking about going for a used couple of speakers, having a 1500$ budget.

I am planning to driving the speakers with my actual amplifier which is a Threshold Stasis 3 with factory upgraded balanced inputs - recently fully serviced and restored (only psu caps have been updated, all the other components were within specs.)
My room is 12x18 (ceiling is 10' tall), with hardwood floor mostly covered by rugs.

Any suggestion?