Cool. There are some details on making an extension in the stos gamemaker's manual but there are supposedly details misingg. There is an example with the missing link extension in the disk. You can get it in exxos' s site
You could also try using old school ripping tools like probe ST , adrenaline ripper etc. I suspect in most cases it may be easier just recording from an emulator as you have done. Also some YM effects may already be available in the SNDH archive as sub ' tunes'. I am sure buggy boy has YM only sound...
The rolling screen is likely a SYNC issue. Prob using 60 Hz on 5o Hz screen? Or an h sync pin issue. A close up of the top and bottom at the rf modulator / monitor port where the soldering is may help the gurus diagnose the issue.
As above I can remember using one with an option to play via printer port but couldn't see it on demozoo, it may well have been the noistracvker player. TCB tracker likely supports this too, as I believe the monster sound cart used this for two channels and ym for the other two.
I should get pastI out on the STE and image up my (1.4 IIRC ) originals of audio sculpture. It would be interesting to know what was changed in v 1.5. Also I think DHS has only up to 1.4. So a genuine 1. 5 is an exciting find!