Hello Suttlaw, I personally modified the SCD-1/777ES based mostly on piece parts and ideas from Reference Audio Mods. Principal improvements to the transport section include Superclock 4 and discrete DC regulation stages powered by a 12V battery. Reference Audio Mods knows how to do it. The migration to a battery supply is not essential to improving performance.
Whether stock or modified, the Sony DAC section is now long in the tooth. Currently the modified transport section feeds RBCD into a repurposed integral DAC section comprised of dual-mono Twisted Pear Buffalo II DACs that utilizes SOTA ESS 9018 Sabre chips, followed by an Audio Consulting transformer-coupled output stage as sold by Reference Audio Mods.
Bottom line, the Sony transport section is very good in stock form but can be improved significantly. Even though the Sabre chips are relatively impervious to transport jitter I've found that the DAC sounds much better with the improved transport.
Part of the rationale for resorting to the Sabre chips is to prepare this CDP for 32bit/384kHz S-PDIF or I2S inputs in the months to come. However even after that I don't think I'll be losing those silver discs...