You want killer bass with the speed to match the Quads? Here's my suggestion, another diy project. Order a pair of Walsh 200 MK-2 speaker drivers from the folks at OHM Walsh. This will run you about $1100.00. Next, build a cabinet of 2.5 - 3 cu.ft. interior volume, ported, tuned to 18hz and there ya go. Order a Marchand 2-way stereo crossover, an amp known for great bass control and you're on your way.
Nick
Nick