Exporting audio in Sibelius 7 with NotePerformer

Hi all,

Not sure if this the right place to post this but......

I just about finished a piece I've been working on (with Sibelius 7 with NotePerformer) for a couple of months now and I want to export the audio. When I play it in Sibelius, it sounds great, but when I play back the exported audio it sounds very heavy, muddy and I tried turning down the base and the master volume but it hasn't really made much difference.

Is there a trick or some way of configuring the mixing panel so that it sounds better once exported?

It's the first orchestral piece I've completed with NotePerformer, the only other piece I've completed with NP was a flute and piano piece and that sounded fine.

Just wondering if anyone else has the sort of problem and any possible solutions

Thanks in advance
Mark