One of the very few digital units I remember listening that shook my firm "analogue" slant, along with the Stax DAC TALENT and Sony's own CDP-R1a & DAS-R1a combo.
I couldn't afford an X777ES then, let alone the Stax, but I own one now - in fact I own two and I really didn't hear the need for a future upgrade for a long time.
As all Sony X7 players, the build quality is truly unbelievable and completely unseen nowadays.
The feel of use matches that quality : one has to see and touch these players to really understand what luxury in build-quality is.
It is no wonder Accuphase used Sony's drives for its own. And no wonder these sold like hotcakes in Germany and Japan : as all X7 players, the X777ES still is part of the crème de la crème when considered as a drive.
As an integrated player... better has been done since, for sure. And better had been done before, too : Sony's own CDP-R1 and DAS-R1 combo, albeit "older" in technology, has all the qualities of an X777ES... times 10 !
The price wasn't the same, though, in a ratio of one to four, and the PULSE circuitry, developed by NTT and Sony, became really better after the X777ES.
The R1 combo did have those magic Philips TDA1541A S1 converters, too.
Analog outputs are available in three flavors : RCA variable, RCA fixed or XLR fixed.
The fixed XLR are directly hooked to the PULSE D/A chips : very tight, very "direct".
The fixed RCA are the center of the show as they benefit from Toshiba FET transistors : sweeter, lush-ness comes in.
The variable RCA have too much cabling (from the d/a board to the motorized volume pot and back) and loose a lot of finesse along the way.
Depending on your preferences and the rest of your units, you will either prefer the fixed RCA or fancy the XLR - both are equally excellent, if in a different way.
Mods abound although not as numerous as the Philips-based Marantz (or Philips LHH) but one can already easily upgrade the original 16.9344MHz clock.
Sadly, in true Sony cost-multiplication style, the KSS-281A inside the X777ES was used only in the X777ES : original spares are now a faint souvenir and the only way to revive a tired X777ES is to find another... preferably lightly used.
If finding X777ESs is easy as that X7 model sold very well all over the globe, finding one which saw little use is more difficult.