Multiband compression on the lows and lowmids can really tighten up stuff. Also, give the kick and the bass their own low frequency to sit at. If the kick sits on 60hz, make a sharp cut on the bass there, and vice versa. Use of hipass filters all over the mix probably goes without saying.
Btw, I'm all for experimenting, but I can't think of a reason why stereo-imaging would tighten up low end. As a matter of fact, I usually keep my low end as mono as possible, since it's not very directional anyway. Care to elaborate on what you are doing?