from what i have heard the the BM's are a lil more on the SQ side but they have pretty good output and the sd2.5 are sql like cheaper versions on dd 2512 this is all from things ive read around the forum
neither one are going to have outstanding sq...never heard the sd..just the sd.2, so based on what i no
sd.2
pros: Very effeicent Nice price tons of output
cons: Lacks low end needs a ported box
Si Bm's
pro's Can be had cheap now since the new ones are coming out sounds better then the sd.2 decent output
cons: Waste unless u port it not as efficient as the sd.2
If it where me, I would look into other options depending on your budget and overall goal of ur setup..if it where between the 2 setups I would get the Bm's