IMO, it will depend on your room size.( Very large and it is a definite, very small...maybe not so much-or at all) With Vandy 3A's, I believe you could certainly get some nice bottom end extension and an increase in dynamic portrayal with a smallish and decent sub. I would think a REL or a JL. Like another member stated above, room acoustic treatment will be beneficial and I would add that first. I would start out with one sub, as adding two is a much more difficult set-up and may not be necessary in your room and for your tastes.
Are subs worth the price for music?
My current speakers are Vandersteen 3A's. I consider them to have a good, solid low end. Specs say 26hz, -3db, if I remember. That's lower than most any music. I'm considering adding a vandy sub, possibly two to the system. My question is, for strictly music, are subs even worth while...$$$......if so, why? What could I expect that's different and/or better than what I'm already hearing..............No experience with subs and music, so forgive the lame question for those of you who already use them.