Thanks for the help.
I've marked this as solved because as far as I can tell, all is working correctly. Sadly I can't be sure if the problem was on the USBUIRT device or related to the TV device template that I originally built (and hacked). The reason I can't isolate is that I deleted all these devices and re-added the USBUIRT and then, subsequently, a new TV template so I didn't isolate the problem. I would put it down to the TV template except for the fact that a related issue (see other thread) of USBUIRT dying on router reload has gone aways as well which makes me wonder.
Nevertheless, all appears well in the land of USBUIRT - it is receiving 100% and transmitting as, I believe, it should although I'm still having lots of fun getting the codes right and ensuring the IR is delivered etc etc. As suggested by Thom, I'll probably invest in a dual-head emitter to target my devices more accurately for a start and, do my level best to get discrete codes. Toggle is a nightmare!! My TV goes on and off all the time to the degree that I've taken the power code out of the template and I'm controlling it manually at this stage!