The RNID Solutions Catalogue Issue 17 in October 2010 introduced the Comfort Audio Listener. This uses the DigiSystem. It is expensive but might be worth looking at if you need it - especially in conferences or meetings when more than one microphone is required. Cash might be available through Access to Work funding. I reviewed the system in July 2009.
I found there was a drawback in that it was not possble to control the DM10 microphone from the receiver. When listening to the main microphone (DC20) unwanted sound from the DC10 was a nuisance and vice versa. It would have been very useful to be able to switch between the microphones from the receiver. The Contego allows one to control the transmitting microphone sound volume so that when listening to the microphone on the receiver unwanted sound from the other microphone is avoided. It was a pity(I thought) that Comfort Audio (who also make the DigiSystem) did not arrange to have this on their, otherwise highly sophisticated, listener.