I support the raw sub (cabinet with driver/s and inputs; no passive crossover built in) in conjunction with an external active crossover and external amplifier. This provides much more flexibility as well as allowing one to place the electronics on the shelf/rack with the rest of the gear.
Mounting electronics inside of a sub has to be about the worst thing you can do. Unless a fairly elaborate isolation/suspension is used to isolate the electronics most eventually fail due to the vibration of the sub. The only sub I've had for more than a year that has not failed, so far, is an old REL Strata. Mirage, Energy, Sunfire, JM Lab; they have all failed; usually just a minor part or loose wire as a result of vibration.
A pair of subs with smaller drivers (say, dual 8" drivers in a push/pull arrangement) would probably be best for the most musical with 10" drivers being the best compromise between "quick" drivers and deep bass. You then run them in stereo which helps with a lot of placement issues.
The Bryston active crossover appears about the best value in a quality crossover but the Marchands are attractive, too, if one wants a tubed unit. There is never any shortage of powerful used stereo solid state amps so that is a no brainer.
Tyler Acoustics will build custom subs; already checked that out.
