All i have to say is "TUBES ARE BAD"
BAD BAD BAD.. here's why..
look at a pipe organ.. how does it work? resonating frequencies.. and that's the problem with tubes, they resonate, so you get these nasty high spots.. they're just bad..
personaly, I have a JL 12W6 with an Xtant amp (175w @ 3ohm)
in a nice thick 1.25 cu/ft box, it's a standard prisim shape, and has aprox 2 pounds of fill. it sounds great, no resonating. I think i would prefer a boston competitor, with a pasive radiator, but i don't have the money right now :(

on the jetta.. I love my 2000, and it was very easy to install on.. the speaker layout is much more sensable in the 2000, (i'm still trying to figure out what's up with the 2 different angles on the dash tweeter mounts on the v3 jettas)

12gig green mk2 -- 080000125