Thanks for your comments Markus.
But - if the 1064 uses the second flexSPI interface for the on-chip QSPI flash, then presumably this means that this same flexSPI interface cannot also be used for external memory? (this was my original question).
External octal hyperflash/hyperram needs BOTH flexSPI instances to work, but you can't do this if one of the flexSPI is being used for the internal QSPI flash.
regards
-Nick