Aggregate HDN/HD IO 16x16 and ULN2

I just got a Metric Halo ULN8 and want to use it along with my HD IO 16x16. In the Audio Midi set up under ProTools Aggregate i don't see the HD IO, only the Mac built in Output so i can only either use the HD IO under HD Native Thunderbolt or the ULN8 under Aggregate.



Is there a way toy Aggregate the Avid HD IO and third party interface like the ULN8 ??? Thanks