When I'm listening to 2-channel stereo, it is sending the lows to the sub. My guess is that most of us here with one system and smaller front speakers do the same. Probably quite a few with larger fronts as well. A good sub, when blended well with your mains, really rounds out the sound and certainly does not detract. The HSU's have certainly received quite a bit of praise for both quality and bang/buck. My EP350 has been a nice performer as well. If you are thinking about an eventual 5.1 or 7.1 upgrade you should consider that while researching a sub. You can buy one now that will blend with your future system. As for overkill: A) Ain't such a thing as too much bass and B) Most subs have attenuators so you can dial them down. Let us know the size of your room and your future plans and you'll get plenty of input from the Axiomites.
