when i load a specific vst synth for a midi track, sforzando loads fine and uses output s2 in the mixer and i can hear the sforzando instrument.

when i load the BBC Symphony Orchestra from spitfire, the output changes to s3 and although the meter shows an output i can't hear the instrument.

what am i doing wrong? i added the BBCSO plugin to the synths available - all the others were there by default. the port is 19 whereas sforzando is port 18.