Nope, that hasn't improved things.
I have established the following-
The first time I start the media director, absolutely before I do anything with it, the UIRT appears to be transmitting - in other words, if I click the "Test Code" button from the web admin / av DEVICES / AV properties IR codes section of my TV (controlled by UIRT) then I see a "flash" on the transmitter.
That works up until the moment I "play media" on the MD. So I can open a media grid (ie go to media->Audio), browse to a track. Up to that point, UIRT still transmits when I "test code". Then, as soon as I hit play and the media starts playing, the transmitter stops transmitting and won't do it again until (I think) the MD is rebooted. Note that I'm doing all this (controlling the MD) from a weborbiter rather than the IR remote in order not to confuse things by using the UIRT as a receiver.
So I have "clipped" the DCErouter log and the UIRT log from the appropriate MD and shown the entries from the moment I start playing the media. In other words, from the moment the UIRT stops working. Here they are:dcerouterusbuirt
So... the usbuirt is the simplest - apart from a bunch of "Cannot find anything for IR 170000F201CA" which is usually associated with IR signals received from an unknown remote/source, the only entry that could be of interest is "#### Pre-Process Queue = 1"
Does that mean anything to anyone?
And then on the dcerouter side, apart from all the subsequent messages showing what music I was listening to, possibly of interest -
"Received Message from 50 ([36;1mHTC Web Orbiter / [0m) to 10 ([36;1mMedia Plug-in / Server Closet[0m), type 1 id 43 Command:[35;1mMH Play Media[0m, retry none, parameters: <0x7bfb4b70>" <- the play media command to the plugin?
Then later " Received Message from 78 ([36;1mOnScreen Orbiter / TV Room[0m) to USB UIRT 0038(139), type 1 id 687 Command:[35;1mSet Screen Type[0m, retry none, parameters: <0x777abb70>
08 02/07/13 6:26:22.292 Parameter 48(Value): 0 <0x777abb70>" <- set screen type to USB UIRT?
Then later "[33;1mMedia_Plugin::CheckForAlternatePipes no destination for EA 3 TV Room[0m <0x917dfb70>" <- ??
Shew.... not much to go on at this stage.