Dual IR emitter should work fine. The output will not be quite as strong as you are sharing the voltage between 2 emitters insted of 1 but you should be ok as long as your emitters are attached directly over the ir reveicer on the devices.

As an installer, I would try it.

You can get these for $7
[Link: smarthome.com]

It's worth trying out for $7 before you spend $75 on a cheap repeater system.