The difference between these speakers is that the 602 has double the
internal volume and a larger mid/woofer speaker. This gets you much
better midrange and bass response. The 602s woofer is not to large that
it messes up male and female voices but this also means that the bass is
not going to go that low. The 601s I think are good for about 75-80Hz.
and the 602s will go down to about 60-65Hz. But even if you get the AS-6
sub from B&W the 602s still sound better! The 601s are somewhat lean in
the lower mids and into the bass end. Adding the sub and adjusting it to
sound the most balanced in the system does not solve this leaness and
even the 602s are somewhat 'English' in character. This is to say that
the errors are of omission as opposed to colorations. All of the B&W DM
60X speakers have this charateristic B&W sound, very smooth and fine
resolution but mids are somewhat polite. I bought 602s with an AS-6 and
am quite happy with them, I listen to classical and jazz with some
insturmental and vocal solos.
Hope this helps.