Good Qualities: Overall very balanced speaker. Very smooth a tad bit of warmth and "bloom". Still not far away from natural. Very natural. Excels at jazz, small to medium scale acoustic music and piano. Overall musical speaker. Most things sound good.
Weakness: Bass. The bass these speakers do produce is enjoyable and realistic but they don't go low. If you a bass head these are not for you. More about resolution paired with musicality.
The inability to do low bass is not a killer but on some tracks of bass heavy music the bass does not stack up well. but its the minority of songs in my collect. The speakers do intergrade the bass they do have well with most music.
Obvious with out the bass you lose impact on recordings and maybe classical and large scales work are not what the could be with more bass.
They other weakness is that some electronic music or heavy distortion or filters can sound bad. Its really a crap shoot because it handles some music with that well and other it just does not do well. It might actually just be a the recording quality as opposed to the speaker.
Overall I am very happy and have thought about moving up the line. While not huge on bass if I start looking at 5-6k I want it.
I have not heard the 50s but just heard there Ranger Series 6k paired with expensive Audio Research tube amplification. I really like the speakers. I need to hear more and personnel don't thing Audio Research is a good performance/cost ratio. I would have liked to hear them with something like Ayre electronics or something more resolving with the Ranges to see how they do. Also I would like to turn it up more to see if I would be satisfied with the bass output.
Heard System Audio with NAD, Audio Research and Exposure.
I run mine with a VPI Scout and Dynavector 10X5. Very happy.