surffish,
I use the Sony AV-3100 and IR543 and find it works very nicely. All my X-10 devices are all on the same house code. Keep in mind that the AV remote doesn't send any house codes, only unit codes. The IR543 sends the house codes. You setup the house codes via the red wheel on the IR543. So if your zones are all on the same house code then as long as your signals reach their intended devices properly (this is the hard part) it should work. I'm fairly new at this myself so if I stated something incorrectly or there are better ways someone else on the forum will help.

Right now my setup is as follows. My AV-3100 and IR543 are in my family room (which is my home theater). I control recessed lights that are on 2 seperate circuits, same phase (circuits not phases) for this room via the remote. I also control the recessed lights that are in another room, the playroom. Again, different circuit, same phase. I also control 3 outdoor floodlights, different phase, different circuits. I'm in the process of adding more.

As I said, the only factor will be getting the X-10 signals sent properly and strong enough. I ran into some problems and with a little testing and the additions of noise filters I was able to be successful.

One thing you might want to do on the Sony remote is if you have a system button or component button you're not using, you might want to copy over the lighting controls onto it. I found accessing the lighting controls via the "Other" button not convienent at all.