I replaced the 4 door speakers with 6.5" pioneer 3-ways from Wal Mart. Took 90 minutes.
Only side effect is you have to bring down the mids & treble because the tweeters are hot hot hot being 12.7 ohms and the pioneers putting out less volume.

Not quite as enjoyable as the original sound of the system, but better than blown speaker noise

FYI-Pioneer makes the Mark levinson replacements from the dealer

 

I tried different speakers in my car, Rockford Forsgate, Infinity, Alpine yet I went back to original ML and glad I did. No aftermarket speakers in up to $150 range sound as rich as original ML. IMHO I'd buy original speakers at Sewell with CL discount.

 

I replaced door speakers in front with Polk audio, sounds much better then stock system in my opinion. I replaced them with the 200$ Polk audio set with a warranty from ABC warehouse just in case they ever blow but they never will. They are some of the best door speakers available.