It might be that the aux outs only go to the patchbay, and the normalised jacks only go back to the 651 (for the cans feeds), it could have been assumed that you'd have a range of FX device inputs wired to spare jacks on the patchbay and that you'd just patch across to them as needed.
Personally at this point I'd have a look under the patchbay! Yes it's a bit of a pig to get in there, but once you're in it should be fairly obvious.
I'm still annoyed that I can't find this information in the manual...
Cheers,
Andy