Found this on TGP from the man himself when he was first releasing it:
Basically, it’s an FY-6 with some extra bells and whistles in a “pedal
board friendly” enclosure. The official name is the EFY-6, with “E”
meaning “Enhanced”.
The “Expander” knob has been renamed “Fuzz”, and the “Balance” knob has
been renamed “Gain”, as these more clearly describe what these controls
do.
We fiddled with the differential amp and worked out a way to be able to
adjust the amplitude of half of the cycles coming out of it. Turn it all
the way down and voila! No octave step up! Turn it all the way up and
it sounds like an original FY-6. In between you can adjust for however
much chord smashing synthy overtones you want. This knob is
appropriately called “Octave”.
A cross-fade knob was installed between the mid-scoop filter and the
voltage divider that used to be connected to a switch labeled “Tone”.
You can now blend between the two tone settings. Obviously, this knob is
called “Tone”.
The final stage got a gain boost so that the maximum output signal level
is more than 4X the maximum output level of the original FY-6, or more
than double the volume.
With the knobs set appropriately, it will sound just like an FY-6. Move
the “Octave” or “Tone” knobs away from their limits and you can get
tones not possible with the original FY-6.
Unfortunately, Wattson Classic Electronics has shutdown, and while they were around they made very few of these. What brought me to find out about this pedal is that the guys of SUNN O)))) have been known to use this pedal.
Set the trimmer to get the octave effect.