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