Glad to see that you have revived your mastering system , it will be interesting to hear what the STB can add to it ! I'm kinda surprised that the stereo cartridge compares so well , or is it the Thales arm that makes the difference ? About the transfers - I'm very interested in the "few things" that arrived in the bunker last year , especially the acetates .
STB adds realism. It improves everything, you could say I suppose. But the main benefit is in the total package of subtle detail, which lets you imagine the music is real, not reproduced, if your mind is relaxed and trained to listen that way. Even if the flacs contain STB detail, most of these details will not be audible when played on a system which has not been treated with STB.
The Kuzma arm has extensive STB coverage of the entire arm tube and housing, but the Thales has none. The Thales can not be treated that way because the two arms which control the parallel tracking of the cartridge must be free to move (see photos). However, I have treated the entire length of the Thales phono cable with the latest and greatest (removable) STB tape, whereas the Kuzma cable is painted with a much weaker earlier pre-STB compound that can't be easily removed. The Kuzma has the Lyra mono (higher outoput) cartridge but the Thales has the Lyra SL super low-output version, which has better detail. With the STB treatment the low output is not a problem, because the noise floor for the entire systemis incredibly low. I recently supplied transfers of a few hard to find 45s (supplied both Kuzma mono and Thales stereo versions) to Alec P who has excellent equipment, and a high degree of technical knowledge and ability. After comparing both he chose the Thales stereo transfers, and mixed one channel down to mono. I decided to leave the Thales installed, since it gives the ability to discard one channel if it is weaker than the other. The drop in output of the stereo cartridge vs mono is insignificant considering the low STB noise floor. The Kuzma arm is still probably as good as the Thales, and possibly slightly better in the bass, all other things being equal. But the other things are far from equal!
The two best acetates I received last year (Groop and Jackals) can not be uploaded, because both were sold to me with the understanding that I would supply the previous owners with transfers which will be used for legitimate 45 reissues licensed from the bands if possible. However there is the Apollos Apaches acetate, which I will definitely upload.
Photo showing the Thales tonearm. The two halves of the arm have to be free to move back and forward as the arm travels across the record, so no STB can be applied to the arm tubes. The second photo shows the Lyra stereo Etna mounted in the Thales headshell.