After 8 years of "no high and no low, it must be BOSE", I finally replaced both front and rear speakers with infinity Kappa series 63.7i front and 52.7i rear, makes it a total 11 speaker (including the bose subwoofer) system. I must say, wow, what have I missed. The subtle bird chirping in the kiddie songs was not heard from the bose speakers before is now clear and crisp. Driving the ML is definitely more enjoyable these days with new speakers and new shocks/springs.
FWIW, I did not replace the head and the bose amp, nor the sub. I had to reuse the bose speaker housing to install the new speaker. Also put dynamat on all doors to improve sound isolation and reduce vibration. 2 nights in the icey cold garage is well worth the effort.

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98 ML320 (gone but not forgotten)