The TA-F777ES topper, like a few other early ES units, was not released outside its country of origin so, elsewhere (everywhere), the F555ES represented the top of the newly (re)launched ES series.
A fairly basic amp if very healthy indeed, and quite a best-seller, too, but the ES line was (re-)starting afresh so the PPS, Heat-Pipe and other old/new/old technologies were banished...
The one reminiscence is the placement of the volume knob : left, just like the pre-Esprit and ESPRIT preamps, thus hinting that these amps also used the "simple signal path" inaugurated with the TA-E88B in 1976. But hinting only : wiring is quite hectic inside and there are no relays to shorten signal paths...
Inaugurated here was ACT (Audio Current Transfer) which uses current amplification to transfer signals from preamp to power amp stage and achieve 120dB of dynamic range and outstanding levels of stereo separation.
Two bigga ELNA For Audio 22,000µF /63V caps and a sizeable Bando transormer take place in a non-Gilbraltar enclosure, the layout of which is somewhat reminiscent of already "old" amps like the TA-AX8 : five "industrial" PCBs, PS to the left, heatsinks at the back, main caps center.
That's why the TA-F555ESII or the TA-F777ES are the real first ES amps.
The TA-F555ES however sold like mad, worldwide.