The audio interface is not needed for importing/exporting, so it's not that.
You'll want to provide a screen shot of your export dialog as well as a section of the track information in order for someone to help you track down the cause,
My first guess is that you don't have the region with audio selected when performing the export.
For example, if your song goes from measure one to measure 50, but you are exporting measure 51, you will get silence.
Or if you are exporting track 5, but track 5 has no data then you will get silence.
Are these audio tracks Instrument tracks or MIDI tracks that trigger external (physical) sound modules?