After all this messing about I thought i'd my system all sorted. The BC6 23 Mk1 is soon away to eBay and a Mk2 arrived today. It's in great condition and the MacMini works perfectly with it. With the Beo4 controlling Plex without issue.
But.... it is giving of a high pitched hum.! I think it's something to do with the power supply... Anybody have any thoughts? It makes no hum until the display starts up. And if I put the contrast way up the hum gets louder.
Thanks, Andrew.