Thanks for the reply John.
It seems that the problem isn't with a pedal being over sensitive, but my cables - 'low noise' van damme cables.
Here are some photos to help you (and anyone else who wants to chip in) understand the situation.
Board 1: The main hum problem on this board comes from the cable going from wah to moog, and another going from moog down to the boss bypass loop return. Moving these cables even very slightly can range from silence to extreme hum (I have tried using different cables)http://imageshack.us/photo/my-images/38/p1010001ck.jpg
The main hum problem on this board is the two blue leads going from the Line 6 DL4, up to the Cathedral reverb. I've had to tape and velcro them in this position as any other hums like no other!http://imageshack.us/photo/my-images/13/p1010004ea.jpg
On Board one, one PP2+ is located here, under the moog:http://imageshack.us/photo/my-images/51/p1010002wk.jpg
and the other here, under the Line 6:http://imageshack.us/photo/my-images/109/p1010003lk.jpg
I found optimum positions for the PP2+s by literally moving them around until I found a place with no hum, and these were the ONLY places!
On Board two, the PP2+ & Digital are placed here:http://imageshack.us/photo/my-images/441/p1010007kv.jpg
& these are the problem cables:http://imageshack.us/photo/my-images/192/p1010005fb.jpghttp://imageshack.us/photo/my-images/580/p1010006cb.jpg
Any idea why they could be so sensitive? I really don't think my cables are abnormally close to the supplies - I can't stop worrying that it is to do with the metal edging on the tier?
NOTE this hum is with every pedal bypassed.