You'll need to run the Fostex drivers out at least 200 hours to hear what they're really like. Most Fostex drivers vastly prefer tube amps or even digitals over traditional solid state.
Your assessment of depth of bass output is probably correct. For 3 times the price Bob Brines offers transmission line floormounts that will go south of 40 Hz. (He also offers plans, panelized kits, or assembled rough cabinets for much less.)
