Pros: Brutally honest and comfortable
Cons: Brutally honest; you may not like some of your favs anymore
Great reference-quality open-back-headphones, big sound stage, accurate reproduction, detailed.
If you have a great recording, you will hear detail you may not have heard before. My digitally recorded version of 4 Seasons, done in a good sound room, it excellent, you are there.
If you have a poor recording, you'll know it.
As to the base issue, my pre-amps have built in equalizers and my equalizers have equalizers so its not a show stopper for me. If you crank up the bass, these will bump with the rest of them.
Yes I mention all 3 up there, I hear very little difference between them with just a tiny bit less soundstage for the 601, and a small dip in the higher mid also for the 601 that is surprising to find in one otherwise excellent headphone, but its is undeniably there. If I have to find something negative to say then it would be that these headphones provide excellent reproduction, but are just a bit dry. In recordings where the room ambience is part, it is a bit muted with these cans.
As seen in my small gallery I am also familiar with K272, which sound quite like the Beyer DT220 both a bit warmer with more solid bass.
I hope to return here with one audition and personal view on the 550 in the future.