what you need is as follows.
1 - mono cable, Tip/Sleeve, this is the guitar output cable that goes from the guitar to the amp/preamp. this is also the cable that turns the preamp on and off and needs to be mono to achieve the switching action needed.
2 - Stereo Cable, Tip/Ring/Sleeve, this is the OBEL cable and is 2 cables in one. it will have one side(a) for the send to the effects, and the other side(b) will be the return from the effects back into the guitar. to achieve the splitting this cable can be
(a) a stereo Y cable with one side as a stereo plug and the other end 2 mono plugs.
(b) a Y adapter which would use a standard stereo cable with 2 stereo plugs and the adapter would have 1 female stereo jack split to 2 mono plugs.
(c) or you can get a network box that is a tiny effect type enclosure with 3 jacks, 1 stereo jack split to 2 mono jacks.
either way you will not get a cable that has all three functions. ie.. mono output and stereo obel in one. a Tip/Ring/Ring/Sleeve jack and plug would be needed, but only come in 1/8" and too small for the rigors it will get. the other possibilty would be an xlr but the preamp switching becomes a problem in that regard.
the best option for the obel is (c).
you can PM if interested in a network box, and andrew at aoguitars.com can do the cables.