Upgrading audio system from Jensen to Bose?

If I were in your position, I would replace the speakers with a decent quality speaker like JBL or whatever your taste prefers. And then replace that headunit with something that will give you some power. (It only puts out 6 watts per channel.) I would use a nice Kenwood or Pioneer unit. Yes I know the mounting holes are not the same, but for a small price you can either built an adapter or have someone else build it. Because your existing unit has the ability to direct music to 4 different sets of speakers (if I read the specs right), I would install a switch that would allow you to control which speakers are receiving music.

Doug