Alientek D8 with i2s?

[the hound of sound]

hello folks
my Alien has arrived and been dismantled.
I read a suggestion that it might be possible to disconnect
one of the inputs to these digital amps and co-opt it's i2s
lines.

as luck would have it the usb input to this amp goes
directly to a daughter board with an xmos chip and helpfully
labels its output pins!
they are GND, SPD, MCLK, SCLK & SDIN.
perusing the i2s spec it would seem reasonable to postulate that
SCLK is SCK and SDIN is SD (serial data).
which leaves SPD and MCLK as candidates for word select WS.
would anyone like to hazard an opinion as to whether it would be
electrically safe to try both?
is it even reasonable to assume the output of this daughter board
is i2s?!

it doesn't look possible to trace the lines to the STA326 chip - having only ever tried my hand once at making a simple pcb I imagine modern fabrication has hidden the lines in an internal
layer.

 

[the hound of sound]

my bad - there were six lines in fact and the one I missed out
was LRCK. aka word select. sorted.

but the mysterious SPD.... anyone seen that acronym before?