best bang for buck on used ht speakers? maybe b&w?

Ok I might have been going about this ALL wrong. lets start with what i have... b&w cdm 1 bookshelf fronts, a bad center, b&w 602 bookshelf rears, cerwin vega sub. pioneer elite 92txh with pre outs for additional amps (if needed) i was just thinking about upgrading to the matrix or first gen nautilus speakers. maybe floor standing or towers. before i get too caught up in the excitement of buying, what are other good alternative speakers or set ups? towers needed? book shelf and a better sub just as good? what is over kill for only ht setup? i was thinking b&w 800, 801, 802 overkill? what ya got?