I understand you are wondering about the DACs in the LD-S1, it being a beautiful piece of equipment circa 1987, I noticed the video only had a S/N of 48dB. I had a player with that video spec for 15 years, and ended up finding a CLD-704 (Which I believe is the same as the elite 79)
Anyway, the 704 had a S/N of 51dB, and although I'm sure it's not the sole reason, it created the best laserdisc picture I've seen. (I've never had the chance to see the HLD-X0 or X9.)
Can the S1 be modified to use a digital output? You could then use the DAC of your choice. I know these are questions you have likely thought about, I'm just curious as to what your thoughts are.
Former USSB uplink operator.