usually two of the same sub are used if you are going for dual. however if you can afford three subs, then you can have the one that is different as the lfe and the other two as powered subs for fronts. this would mean that the lfe sub would be the better one (especially for ht). i have used that setup in the past for some fronts that i liked but didnt have much bass, so i got some decently priced subs for the fronts to go with my other sub. this will do a lot more for you than two subs by themselves. i dont know what you have heard, but low frequencies are omnidirectional (you cant tell where they are coming from), there is a frequency (i forget what it is) that below that you cant tell where the bass is coming from. so in theory two subs handling lfe is not much better than one that is 2x better, if you catch my point. i.e. get one better sub rather than two lesser ones. i mentioned the using subs for the fronts to handle bass, albeit a little higher frequency bass that you would want to come from the fronts...