I'd like to try and control my fireplace on/off and lighting on/off with my MX700. Would it work if I bought 2 IR543's instead of one IR543AH?

Do you need more than 16 items to be controlled? If not, one IR543 will work fine.

I have one fireplace and one set of lights I would like to control, but separately, meaning I might NOT want to switch the fireplace on with the lights at all times. Would the IR543 give me this kind of control ?

The IR543 will allow you to control 16 seperate devices. You could control 15 lights and your fireplace if you wanted. If you wanted to control more devices, you would need another type of IR to X-10 converter.

have you seen this thread:
[Link: remotecentral.com]
i have a description a few answers down from the poster. i use a universal module for my fireplace switch so it does not respond to "all unit on" but it does respond to "all units off". ok by me. i would rather it turn off by accident than on.
good luck.

Don't ever try to use 2 IR543's in the same room. Remote controls just send out unit codes 1 through 16 so if you try to use an IR543 on House Code "A" and one on "B", when you send 8 ON both IR543's are going to respond. The IR543AH has had it's house code replaced by an IR controlled dial. With it you can send a House Code, kind of like getting up to turn the dial, without having to get up.

If you use scenes then the AH is probably overkill. It will also only work with a PC programmable remote, or with a universal remote taught by one.

Bill
www.homeautomationnet.com