I picked up a peavey cs-400 (not cs-400x) which has been lab tested to clip at 2x266w RMS at 4 ohms per side. I'm currently running just one side of the amp into a 6 cubic feet ported at 35hz isobarically loaded 2x15 cab built by myself. I'm reasonably satisfied at the sound qual but I'm wondering what to do about loudness factor. Not that it isn't damn loud for my bedroom when I play normal music through it (obviously more brutally crossed over) but my original and current plan is to get another two of these 15's and cram them into about 6-8 cubic feet (bearing in mind that each isopair only needs 3 cubic ft) so I could maximise both sides of the amp. Is this a wise idea or would I benefit from just getting new, more costly drivers and less of them in terms of loudness (assuming that the amp was being drove to basically its limits). I play a 5 string so I do need good low response which I get from the woofers. On a side note the subs are 94db/w sensitivity and have 120w RMS power handling per speaker.