Is it possible to use my G-System to control the tempo and preset change of the Flashback X4 (or Triple Delay)?
It is not possible for the tempo:
the Flashback X4 and the Flashback Triple Delay only respond to MIDI Sync, and the G-System does not send any MIDI Clock.
The G-System can only send TAP via MIDI CC, but unfortunately the Flashback's do not support MIDI CC.
It is possible to recall the presets with the MIDI mapping OUT feature of the G-System. You will be able to specify and send one of the 3 MIDI Program Change messages that can recall the any of the three Flasback's presets