kofibaffour: The pressing you list first (above the DCC version) is the Analogue Productions stereo version, mixed by Mark Linnett and mastered digitally. AP also produced a pure analogue mono version.
The main selling point of the new 1-Step pressing is the source that was used to cut the lacquer: The new 2-track master The Beach Boys created in 1972 from the multi-track tapes (1" 8-trk. I believe), with improved EQ (he original is, as @slaw put it, rather dark sounding. I would add veiled and soft as well). Once again, it was the 1972 tape that was created and used to make the version of Pet Sounds included in the release of the Carl And The Passions album.
In the panel discussion someone mentions that the price of that 2-LP package is now selling for around a hundred bucks. Well, a hundred bucks will now buy you the upcoming 1-Step album, which Fremer says is considerably better than the Carl And The Passions version. While both use the 1972 tape as their source, the 1-Step is being manufactured to a far higher standard than was the CATP pressing (made during the oil embargo, a serious situation for the LP pressing business).
I hope the 1-Step makes more audible Brian’s piano notes, which are barely audible in the 1966 mix. There are also 3 bass parts (!) in some songs: acoustic upright, electric, and 6-string electric, as well as a cello, which makes for a pretty "thick" sound. It was hearing Pet Sounds (as well as James Jamerson’s bass playing in "What Becomes Of The Brokenhearted", with it’s exquisite use of inversion) that Paul McCartney credits with opening his mind to the possibilities of his main instrument. Listen to the difference between his bass playing on the Rubber Soul (pre-Pet Sounds) and Revolver (post-PS) albums. A huge change! George Martin was also VERY impressed with the songwriting, arranging, and production on Pet Sounds.