Here's the hacked-up multiswitch. I've removed the chip, and the two transistors that dealt with the 2-way communications over the downfeed coax, and then added +12V, GND, and four control wires.

There is also now a 1000pF DC-blocking capacitor on each of the four coax inputs. I opted for non-surfacemount to begin with, because they were 1/3 the price.

The wires will all go to a USB/GPIO subassembly, for software control from MythTV. Later today, I hope.

Cheers