I think the bass goodness is due simply to cabin gain, and is kind of inherent to most hatchback sports cars. The drawback to vettes as SQ cars is they are real rattletraps, particularly the dash and doors. I stripped my 86 down to the bones and spent six weeks putting dynamat, modelling clay and spray on undercoating everywhere before I put any gear in it at all.
I was especially proud I was able to do each floor pan side with a single uncut sheet of super dynamat, tight as a drum.
Best deal on the 80's vette.... put horns on top of the dash. Slice em down so the dash is the bottom wall of the horn, and the motors go where the factory speakers were.
Also the storage container on the passenger side makes a nice little sub enclosure.