I think the real issue here is what type of amplifier are you using? Accurate reproduction of low frequencies requires a lot of power. This is why most powered subs will have dediacted amplification of 200 watts or more (preferably). Adding a well-made subwoofer to your system will free up your main amp and allow your speakers to open up. HOWEVER, for the same expense of a good subwoofer you may want to consider a heftier amplifier. It sounds like some experimentation is in order. I went with a subwoofer to get that extra low-end punch but a lot of my decision was based on the fact that I wanted to have a HT set-up also.
Great sound possible using a Subwoofer?
My speakers are flat to 38 hz but I feel I'm still missing impact, power and weight on most of the pop/rock CDs I listen to. I don't know if a high quality subwoofer would be a positive addition to my system or just add unrealistic bass and muddy up my midbass and midrange. If anyone has extensive experience with this dilemma please tell me what you think. (would better isolation of components, cables or power conditioner help the low end?)