Okay, what I got so far:

It's a pretty simple board. Will consist of connectors:
1. DB9 for the serial cable.
2. 10-pin header for the ribbon cable, and
3. An as-of-yet-unchosen power connector.

Parts it will contain, will be:
1. The MAX233 (or MAX233A). This is the RS232-TTL converter chip, used after recommendation from the display thread.
2. The power regulator - uA7805. In theory, this can pump as much as 1.5Amp thru it, and take up to +40V.
3. Assorted caps and a diode - the caps for the power reg, and the diode to protect the reg. against any negative spikes. (recommended in spec sheet, adds insignificant amount to board.)
4. A DPDT switch. Why? Well, it will flip the TX/RX lines going to the DB9 connector. In case someone wants to connect the board straight up to the Empeg, or use it in their car, connected to the cable out of the sled.

That's about it. It can be pretty darn small, honest.Forget anything? Me? Probably.

I have some of the parts on order, right now I'm in a crash-course learning a PCB layout and designing software, (and that's where my thanks to PCA comes in.).
Next step, once I get parts, will be to make a little prototye circuit, and connect it up, see if I break anything.

Me.