Interesting comments, theendofday. I haven't heard of the redirected "mono" bass being referred to as a "loss of bass" before - in fact, the reasoning behind bass management is that speakers (even tower speakers) can't reproduce low frequency material effectively (the DM604's output will have dropped 3dB - a halving of the actual volume - by the time a signal is at 39Hz). A subwoofer with a -3dB point that is 10Hz, 15Hz, or 20Hz (or more) lower than that will provide more bass than the speaker alone. With a single subwoofer, you will get a mono signal, but the general concensus I've always seen is that bass is not generally directional until you get above 80Hz at least.

Bi-amping or tri-amping with active crossovers is certainly an ideal design approach. Actually doing it, however, is often prohibitively difficult. Soundhound here in our forum has done it, and built his own crossovers to do so, but the know-how to modify a commercially-made speaker in this way is significant. With DIY speakers (such as jhenderson is doing at the moment ), it is a different matter, of course, since in many cases the DIY speaker builder is dealing with crossover circuits anyway. The benefits of passive bi-amping alone for a speaker are a source of much debate, and the Rotel amp in sraber's system currently is pretty hefty, such that bi-amping may not add much or any benefit. I get the impression, however, that when you say "passive bi-amping with another powered large driver" you are referring to stereo subwoofers. That is an approach that many people use and enjoy, and one that can be implemented with commerciall available equipment. For example, setting the mains to large and placing an Outlaw ICBM or a pair of Paradigm X-30 crossovers between pre-amp and amp for both of those channels, using the subwoofer output of the analog crossover to drive the stereo subs. Of course, you still need to add a pair of subs to the equation, as well, so while all of the equipment is available off the shelf, the overall setup won't come cheap.