I finally began how I always do: I take a scrap of paper from the recycling bin, usually an envelop, pour myself a cup of coffee, and draw out what I envision. In this case, I measured the stereo and drew the number of panels I'd need.
The main difference between this stereo cozy and the toy shelf cozy I made for my son's room is that I made the back panel short so that we could access the cords (to plug in the iPod--we're not that behind the times!). I also cut an extra carpet square made by FLOR that we had to give the top some structure since the top stereo component is smaller than the bottom one. You could also use a piece of foam, Styrofoam, or even just cardboard from a recycled box.
So there you have it--a baby-proofing solution that doesn't require a plastic gate that, in my opinion, just screams "Get past me. I dare you!" instead of "Not for babies please."