Hello Nick,

I am sorry to tell you this, but this does not sound good. To me it
sounds like a broken filter chip. Appearently the filter dose nto work
as it sould do: The example

> Polyphonic mode, triangles with resonance fully up:
> http://www.guitaraustralia.com/MonoPoly/trianglePOLY_resUp.mp3 206KB

shows no resonance at all, but feeds through some portion of the input
signal to the output.

Does the filter basically work What happens if you turn the cutoff
frequency potentiometer full counter clockwise

You might check, whether the SSM 2044 on the filter board is socketed
and perhaps the chips got loose in the socket and needs to be reseated.
If the chip is soldered direct to the pcb I think it is broken at all.

Florian