The SM models have already been discussed before on this site, perhaps you can search the Archived messages.
Infinity made MUCH better hi-end speaker models. Or even the Q models which are great. But you wont see much mention of SM models on sites like
www.bobbyshred.com/infinity.html
The SM models have large woofers and theyre very efficient- so they can be played LOUD w/o requiring a huge amount of amplifier power. If you like to throw parties and blast music, theyre suitable for that. If you aspire to hear music in a manner thats considered "high fidelity", it wont really happen with the SM's. Infinity built other speaker models for that purpose.
Yes, the 15" woofers put out alot of bass. But, its unmusical boomy, flabby, one-note sounding bass. Not tight bass which is the desired quality. There is also not much of a Sounstage/Imaging presentation. They sound "Wow!" at first but their shorttcomings soon become apparent to the ears. And it should be noted that the SM's use the polycell "eyeball" tweeters, and not the much better EMIT's.
If you can get the SM's for very cheap and you happen to like them and their sound, well thats fine, youre the one who should decide for yourself if theyre your cup of tea or not. I'm just letting you know what their basic reputation is. An alternative, if you want strong sounding bass, is to check some of the Infinity Kappa or RS models.
B/F