Great q., as I am looking into that myself (I have a gallo 3.1 (5.1?!) system on order). The way I look at it is, if you are GOING to use a sub amp in order to have the speaker sound full range, then using the Gallo amp is the way to go, but as Grims states i would still use a SMS. My negatives about this arrangement are that bass frequencies are STILL tricky in most people's rooms, so where you put your monitors may not always be the best place for the sub freq., regardless of the SMS (which should improve things 2-fold. I also think that using a seperate sub will allow the main speaks to play all the other freq. with more ease. I guess another consideration is, if you will beusing the system for mostly music, like i am, u would want a pretty quick sub.
-Just my 2 cents.
Please let us know what you chose / do.