I listened to a few discs last night and here's what I found:
The Brooklyn recital was a previously unreleased recording from 1967. While the performance was excellent I found the recording itself to be unremarkable. While a quiet recording the piano lacked the percussive bite that gives the instrument so much power. This may have been due to any number of factors, but it's not likely to make it into heavy rotation for me.
For pre-1942 recordings I played a couple of selections with mixed results. One was an arrangement of Danse Macabre that was originally recorded in 1942 and the transfer sounded like it was from the playback of the original LP (surface noise and periodic ticks included). I tend to filter this stuff out as I listen to a lot of vinyl, but I can see where it could be annoying in a system that can emphasize the upper frequencies.
Another one that I tried was the Brahms Piano Concerto with Toscanini and the NBC Orchestra. This was a quieter transfer, but the recording itself made it sound like I was listening to a recording of the performance played on an old console radio. Even the liner notes for this one stated that it was only released due to popular demand and that it was well below the technical standards of the time. Sonic issues aside, this was a wonderful performance and I found myself drawn in regardless of the technical deficiencies. A shame really as had this was an excellent performance.
Granted, this was a very small sampling of the set and I'm sure that the bread and butter recordings are of a higher standard, but if your interest is in the historical works then you'll likely be disappointed with the sonics, especially given the cost. This is unfortunate as the Heifetz collection, which I've explored more thoroughly, has surprisingly good sonics on the older recordings.
As an aside I found that two of the three discs that I played were noisy in my player (as if the disc itself was out of balance). The Boulder spins the disc at a faster rate (up to 8X) so as to be able to read ahead while still performing error correction and this may have been the reason for the additional noise. Odd, though as the thing has always been dead quiet otherwise.
Let me know if there are any others which you'd like me to spin up.