Hello @greg79 ,
It should be possible to develop a USB Composite device consisting of audio and serial USB interface (by which I think you mean CDC Class) with PSOC 5.
The following document describes how a composite device descriptor can be created: Implementing-USB-Composite-Device-with-PSoC-3-PSoC-4L-or-PSoC 5LP
You would need to use the Interface Association Descriptor (IAD) which is used to describe two or more interfaces (audio and CDC in this case) that are associated with a single device function. More details on IAD configuration can be found in the following document: USB Interface Association Descriptor
The audio class would require you to use isochronous transfers (that have pre-negotiated bandwidth on the bus) that would happen continuously if there is data to send. On the other hand, CDC class will support Bulk transfers which will happen only when some bandwidth is available on the bus. In this case therefore the delivery time varies depending on how much bandwidth on the bus is available.
Best Regards
Ekta
