I'm currently using a 10 year old "speaker package" - Infinity with a sub with 2 satellites. The connections now go from the "speaker out" L & R to the sub, then the sub to the two front Infinity speakers. I'd like to get a "real" sub. Am I correct that would be a noticeable improvement to movie sound? I don't need to rattle walls or anything. The room is maybe 15X12. I've got a Marantz receiver with a sub out jack. Any thoughts on a reasonably priced subwoofer? Also, If I do add a powered sub, can I still use the two infiniti's hooked directly to the speaker out jacks, since they were designed to run off the old sub? Or would I be better off buying new front speakers as well. I was looking at the Cambridge Soundworks Basscube 8 - Any good??? Other choices/considerations please.