Hey I've got a Macintosh MC-420m in my BMW 318, and it sounds good but was wondering if The switch to a Zapco 360.4 might net me slighly flatter curve. or am i going at from the wrong perspective.I am really an spl Guy but my wife wants me to build her an SQ stereo in the bimmer so we can both compete at the shows together.....any help for a newb is great thanx in advance.

macintosh sucks, get rid of it and give it to me... it would match my mac nicely.
seriously now, i doubt that the Zapco would outperform the Mac. even if it did, i think you would be hard pressed to hear a difference. stick with a good thing if its worked for you.
but if you decide to sell, do give me a call!

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Sublime Simplicity is all too rare 92 300ZX TT stage III

McIntosh and Zapco amps have similar tonal characteristics - I'd leave it all alone.