OK Mac I think you are probably right.
I just noticed that with Realband the output is all coming from the audio feed on the mixer with no feed on the midi channel.

I've just tried the same setup using B&B and it works fine (all in tune) with a feed from the midi channel with violins/cellos and Realtracks on the audio
channel on the mixer. So looks like I stick with B&B for the time being.

Gee, it sounds great on some decent big speakers!!