i have my btl 15 in 3cubs @ 33hz. hit the lows AMAZINGLY and still hits the upper notes just fine. The low low notes like 25hz-30hz it doesnt play, but honestly i dont miss it. This box plays low enough to play ludacric blueberry yum yums with baby aborting authority so thats low enough for me. musically its great. possibly a hair bit small so if i were you i would do 3.25cubs @ 32-33Hz and you'll be set man. some people have it in as big as 4 - 4.5cubs but i think with the smaller box you'll have better response on the upper notes while maintaining the beast lows. other factors like box positioning, how close the cone is firing to the wall of the trunk, backseats up/down, etc will contriibute to the bass response in the car.....but usually if you have the box and install right you're set.
I've had numerous setups in the last 6 years, but nothing makes me happier than 2.5kw or more on a single beast sub. get the btl and call it a day. when i first installed mine the suspension was stiff and it didnt play the lows right off the bat, once it broke in it was sweeeeet sweeeeet music all day long.
and as far as sound quality. pretty much every "spl" sub ive played with in a well built low tuned daily box sounds just as clean as anything else. my btl sounds just as nice as my old xxx 15 did. its all in the box and install. hope this was helpful. my kx 2500.1 and btl combo is AWSOME, i'm sure if you go the same route you will not be disappointed.
