Thanks for the pointers I will take a look.
I have also investigated further with my modified descriptors I am seeing many of these interrupts:
USB_OTG_GINTSTS_OEPINT/USB_OTG_DOEPINT_NAK /*!< NAK Packet is transmitted by the device */
The interesting thing is that from the hosts side everything is fine, I have sniffed the packets and all the ISO frames have a success return, I see no difference apart from sizes between the 2 channel and 8 channel from the hosts perspective,
Searching for USB_OTG_DOEPINT_NAK doesn't bring up much but I am pretty sure it is nothing to do with normal USB handshaking, who knows!
I'm guessing somewhere the middleware is saying well you aren't supplying the data I will take over and return valid data, it is very weird.
I will take a look at your links...