I don't disagree with you at all. I thought you had 18 inch woofers. Also, I guess I really didn't make my point above. My point is that a large woofer will (should?) have more trouble reproducing the higher frequencies. 18s, taken by themselves, will not produce the higher octaves as well as 15s or 10s and it's these higher frequencies that define the timbre of a bass guitar or a bass drum. I think it's also the area in which the sound becomes directional and the stereo effect begins. My guess is that your midrange drivers crossover nicely with your subs. When listening for the bass separation imbedded in the recordings you're discussing, are you sure it's the fundamentals you're hearing or the first few overtones (harmonics)?

A good bass driver needs to be stiff and have large excursion ability. This is at the sacrifice the midrange capability of the driver. Combine this driver with a properly tuned cabinet and you can get good low extention. The size of the driver is less important. I think you can go with smaller drivers, or a combination of them in the case of a 2-10, and still get good low frequency extension and efficiency. The 2-10 I use for bass guitar has better low frequency extention than the 15 inch cab I used to use because of the construction of the driver and the design of the cabinet.

I'm not trying to knock your idea here. In fact, I'm going to try it if I can get rid of my family for a day or two. I can setup two 18 inch bass bins and two 2-10 bass guitar cabs. I don't know what the measured response of the 18s are but my 2-10 cabinets are +/-3 dB at 41Hz and -6 dB at 31 Hz, discounting room coupling.