This is a beautifully made piece and here are some pics of the important parts.
In looking at it I saw that the cutting stylus didn't seem to fit snugly in place which could explain the reported dark and lifeless sound. Below is the ruby cutting stylus holder with the nicrhrome heating wire.
This tapered piece fits into a bracket attached to the drive system.
this interface didn't seem as structurally sound as it should be and closer examination revealed a problem. It seems that there was a small 'ding' in the receiver hole making it somewwht less than round.
this minor dent kept one side from seating properly and gaps on either side can clearly be seen. given that the irregulariy is only about 0.001" it will be quite easy to clean up.
For reference, this is how tightly the other side fits.
In general the aluminum piece does not have the 'watchmakers quality' that the rest of the unit has so I suspect it was a replacement part. Once I get the word to proceed I will clean it up and get it back to Pete to cut a few lacquers and see if things improved.