I've found a couple of changes to the opera.ini file that fix this, for the RTE (Irish) stations and BBC Radio Five Live.

I've described them at the help page on my (very, very basic!) Nokia 770 radio tuner site at Radio Ten.

There's still plenty of RealAudio live radio streams that don't seem to play at all, I've listed some of them there. If anybody knows how to tweak the tablet to play them it would be helpful.