SU-A4MKII controls:
SUPER TREBLE:
50kHz (±10dB) / 8kHz turn.
TREBLE:
20kHz (±5dB) / 2kHz turn.
BASS:
50Hz (±5dB) / 500Hz turn.
SUPER BASS:
20Hz (0dB - +10dB) @ 75Hz or 150Hz turn.

The images posted on the pop-ups accessible above come from a 1983/84 catalog that shows both MKI and MK2 versions on the same pages, therefore indicating a longer lifespan than Mark's listing for the MK1 units. By 1985, however, the MK1 were gone.

Technics SU-A4MK2
Technics SE-A3MK2

Inheriting most of the research spent into the invisible SU-A2 and SE-A1 monsters (1978), these were to become the big ones from Technics, funnily being for awhile in the lineups at the same time as the non-MK2 versions...
Considering the specs, the MK2 preamp is a little lighter, smaller and has better S/N ratio (small margin) while the MK2 amp adds a little more electronics (Computer Drive Monitor), bigger caps and more power.

Adrian, who owns three (!) of the later SE-A5 has useful and extremely detailed descriptions of the Computer Drive Monitor system right here.