So I was thinking about implementation of PO sync in OP1, which uses one channel for syncing and other for sound and got an idea, how you can hook-up OP1 to external chain of effects and have dry\wet controls over them right on OP1 for each track.
Simply take mini-jack -> L\R jacks cable. Minijack to OP1, Connect L to effects, R to "clean" channels. Now set all tracks' pan to full right. Changing panning will route more sound to fx chain. I was also thinking that some monojack->stereo adapter might be useful, but considering that it will require external mixer anyway, its not that important.
I think it's pretty basic stuff, but someone might find this helpful. At least it allows you use effects only on some tracks, not on whole audio output from the OP1.