difference between Sony SCD 1 and SCD 777ES

A post of 6/12 asked for comment on the Sony SCD 1. That model was followed shortly by the SCD 777ES, also a two-channel unit. The latter's price was significantly less and later dropped a bit more. That prompted me to add it to the system and I have been pleased. Still, I've always wondered about its construction differences with the SCD 1. The dealer at the time said there were none that they could find, but I didn't give that much weight in my decision. And, I wonder whether upgrades are as available for the SCD 777ES as for its pricier predecessor. Any help would be appreciated. It is being played through Threshold S550E amp, Threshold Fet 10e preamp, and the old B & W 801 Series 2 Matrix Speakers. Those components are a bit dated, but they sound pretty good.