I don't know much about the imprint system, but I think you won't get a dramatic gain in quality from swapping headunits. Deaden the heck out of your car, work a lot with your speaker positioning. Try out different placements for your tweeters, different aiming, and find what's best. If you can angle your mids towards you rather than facing each other, that might help out with staging too.

I just did a small adjustment to my kickpanels (about 10~15 degrees to the orientation of the speaker) this weekend and the stage went up about 6 inches and the depth increased a lot. When listening to Sara K.'s If I could sing your blues, the trumpet sounds really far in the back.

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