Active Subwoofer Crossover

Thanks for the response. I don't have subs anymore and I sold my Aerial 7Ts. 

The Bryston will add the versatility and open the option of dabbling in an active full range set up down the road if you get the notion. Marchand is one other good make and offers tube and SS options. MiniDSP is another worth investigating. http://www.marchandelec.com/  http://www.marchandelec.com/articles.html

I'm getting Monitor Audio PL-500 and hope I don't feel the need for subs. 

I do not find that subs are always "necessary" meaning I don’t always have an irresistible "need" for them with certain full range speakers that do quite well covering bases effectively. That said while knowing full well what can yet be obtained by adding them makes the urge to add them that much stronger. It could be argued that desert is not necessary but its results are obvious while enjoying that big piece of double layer cake along with your favorite ice cream.

There is an active add running for the Bryston here on Audiogon. 

I received my Monitor Audio PL500s and I'm so excited that I don't "need" subs. Yes, subs made a difference with my Aerial 7Ts, but there is something about a "full range" speaker in a relatively big room that a smaller speaker with subs just can't duplicate. I have so much respect for the Aerial 7Ts, but I realize my room is just to big for them.