Thanks for the imput eugovector. More than an exact budget I was curious to know if in genral terms the interesting flat answer / pricefound in the studio monitors (apart from the advantages of being active) vs hi fi speakers, was also found in the subwoofers. Also note that the 2.1 I have intention to build uses them (still trying to decide between MSP 7 Studios or Solo6 BEs).
Regarding the sub, I'm almost ready to choose a Tannoy TS10 wich I have find a good deal, here in europe.
The specs in the m-audio look to be too optimistical (they state a low freq. of 20hz), and since I have not find any tests abouth the sw-10 nor the bx10s, I opted to choose a 'safer' option. Anyway I don't know in how extent does happen what you say about the studio monitor pointing for more spl than low freq capabilities (if I have undertood you correctly).