B&W 603 S3 verses DM 640

I would lean towards the 603...the 640 had some issues regarding blown tweeters...and Stereophile raved about the 603...just my bias...I don't think B&w becomes truly magical until ones hears a model with an exposed tweeter on top...best of luck...fwiw... The 602 is far more common and cheaper on the used market

The consensus at the time was that the 603 was a much better sounding speaker. I never heard the 603 but I did own the DM640's. The 640 has a nice kevlar midrange driver. The woofers are boomy and inefficient. They need quality power to bring out the bass. The tweeters are very hot. Bottom line: The 640 sounds lifeless at low volume and decent but ear bleeding at higher volume. Image focus is poor to nonexistent. Nice midrange.