Improving Carrera Audio (swore I wouldn't do this...)

[r-mm]

For the first 6 months I owned my 87 coupe I didn't turn the radio on. Love the sound of the car, always had the sunroof open. Now I'm doing some longer drives and finally got around to replacing the disintegrating original speakers with Pioneer replacements (their top of the line series D in the front and the so-so A's in the back because the D's weren't available in 4x6.) . Still, just 4 speakers in their original sizes. Original Blaupunkt Reno. Sound is really not so great. Using a tape adapter to play the iPhone sounds even worse than the so-so radio reception. What are my options?

I REALLY like the retro vibe of the Blaupunkt and there is no way in hell I'm cutting any additional holes for speakers anywhere, or suffering aggressive teenage looking grills or the like. Don't care about bass. Really don't want to add an amp or anything like that. Is there any hope for better sound? I guess this just leaves the headunit, or maybe even better 4x6's in the rear?

I think some of you here had a pretty good looking Nakamichi head unit with sympathtic illumination. Would this make much of a difference?

Also, is there any way to adjust the f/r balance with the stock setup? The headunit just has L/R fader. I installed the front speakers first, and when turned up they sounded very good. Then I added the rear speakers and noticed that they overpower the fronts and don't sound as good, plus its sort of odd to have more volume from the back. Does the stock setup have an amp? I though I recalled seeing pics of a Reno + Amp for sale and wondered if this is a std setup.

[r-mm]

SORRY misposted in for sale. Please delete.