Most MIDI implementations I’ve seen use only 3 conductors, so that leaves 2 conductors for your DC if you were using a standard MIDI cable. I think from your post that you already were thinking this, but I wasn't sure.
Yes, I was planning on using only 2 conductors per MIDI connection (IN and OUT), possibly even try it without a screen but I'm not sure how reliable that would be.
Maybe Canare L-4E3-P would work for this application? Two pair star quad.
Looks like it might fit the bill but it's hard to tell from the information on the website (wish they'd put up a high-res picture of a worked open cable) and if it will be light and flexible enough.
Just another thought, maybe you've already run down this road and it isn't an option, but just in case... All the guys I know who use a keytar just use it as a controller for another keyboard. That way all they have to do is run one midi cable from the keytar back to the other keyboard. Power is done via batteries. I actually ran across one guy at a gig a few years ago who had a wireless midi thing. It was a custom black-box deal. It worked great till he biffed it jumping off the drum riser and smashed the keytar.
I'd love to go midi-only but there are some sounds in this particular Keytar (Roland AX Synth) that I really like which I'm not sure I can get from the rest of my rig. I'll have to look into that before deciding whether to go audio, midi or both.
I'm aware of wireless MIDI solutions but this cable is kinda meant as a backup in case the wireless stuff fails.
Having said that, does anyone know of a decent and affordable (say $500 max)
stereo wireless solution? Yes, I really really like to have my sounds in stereo if at all possible. A solution with a plug containing the actual transmitter a la Samson Airline would be nice but I've heard good things about Line 6 digital wireless solutions and I'll accept a pack if it gives better quality and reliability. So far I've only seen mono solutions though and I don't really want to walk around with 2 body packs (3 if I do add wireless MIDI as well).
The whole idea of a (wireless) Keytar is to be able to move around on the stage for a change. Having two or three bodypacks or a heavy multi-channel cable is not going to help in that regard so I need a light and flexible cable and/or a sleek wireless solution.
Thanks for all you comments so far, appreciated. I guess I should first figure out if I'm going to do midi, audio, or both.