Sugabrie is right but prices are pretty high,Wouldn't go with a B&W sub or Velodyne etc for music.REL,Martin Logan etc get excellent speed and pitch accuracy by using multiple small drivers.I think that the Vandersteen 2weQ is oine of the best valuies in High fi$800 for one used $1200 (?) new.Has three small drivers that are muiscal where ars unless you spend meha bucks on large driver sub it will be too slow.Cool thing about Vandersteen as well is it's x-over which is designed for you to hook wires together with your satelites at speaker posts'X-over "see's" whole waveform of muisc not just what is low passed under 150 (or what ever) Hrz and results a a suipperior product at a bagain price.Never was big fan of their well selling 2Ci m(* though big ones are good and costly) but subs are so good that many folks get and at the price end up with a apair.I knwo it shouldn't make sense because you are not supposed to localize bass beneath 150 hrz and therfore only need one but hoowk two of them up and you won't want to give it up.NHT made a good two chanell sub.Depending on your speakers subs are worth it oenor two remeber but way to many folks foget the name is SUB woofer and turn them up to loud and set the crosover too high so they "hear what they paid for".You shouldn't "hear" the sub.It should provide a foundation.If you chosee a value amp don't get sucked into cable snake oil and hav smaller two way spoeakers you'll have better imaging than a larger cabinet.Some of the best b\valuies in Hifi seem to be the hybrid integrateds by companies lie Unison and Pathos.Digital get's better and better so my mind is save there and update that when finaces allow.
Chazzbo
Chazzbo