Ctatham,
The issue with your Signalinc repeater may be that it can't repeat "extended code" commands. This is possible since this is a Smarthome product and Smarthome does not use "entended codes" in any of their X10 Line of products.
Both Leviton and ACT have used the extended code protocol extensively in their X10 products for scene activation.
I have a Leviton HCA02 repeater that is designed to repeat the extended code protocol. I cannot, however, recommend this unit due to it's problems in dealing with standard bright/dim sequences. I can't use standard bright/dim without locking the system up - I use only extended code dimming. Since you have a mixed system (standard and extended code capable units) this would likely be a problem for you.
The ACT line of repeaters is well respected on this forum. I suspect that these units are extended code capable, but would look for another forum member to confirm.
Anyone using a ACT repeater with the LM14a interface?
Boiler