Hey Andrew, I've recently helped Dennis wire his IB5 and the PBG needs correcting. The stereo jack should have one connection to hot and earth and one shouldn't be used, unless as you say you used a stereo jack.
I found another diagram ages ago I used for my IB5 but not happy with it.
If I get time I'll look for a better diagram, but Weirdy may be able to knock you up a diagram for 2 vol, 2 tone, no switch and stereo output jack