i have 2 8's in a very well built box + a lot of dynamat in the rear of my vx and the bass sounds phenomenal

what do you mean by they sound like crap? more elaboration on that would probably help, if you are getting popping and cracking.. probably bad head unit ground, as far as i know, the VX head units dont have a true ground, they ground out through the frame of the unit, so that could be an issue

other than that.. the speaker placement isnt the best in the vx.. did you re-use the stock locations? re-using the stock tweeers along with 2 ways might give you a bit more tinny sound, but i ran mine like that for awhile with no real problems