Great to hear that you are interested in an H9000!
There is not really a "best" connection in this scenario, but with the Antelope interface you would have some great options for I/O choices.
If you use ADAT to connect to your H9k, you would be limited to 44.1 or 48kHz sample rates, and you will also need to clock the H9k and audio interface together.
The DSUB connector would not require clocking since it is all analog connections.
Note that you can use the analog DSUB connectors on the H9k in tandem with 1 choice of digital audio connector (in your case you could chose ADAT or S/PDIF.) So you could potentially have 8 analog channels and 8 digital channels using ADAT all at the same time.
It all depends on your setup and how many channels of processing you need, but you would have many choices with this setup.
Let me know if you have any other questions.
TylerShow More...Show Less...