MR816CSX - No sound with FireWire port 1

Dear Steinberg Users:
I am currently experiencing some problems with my MR816CSX (crackling noise) which is why i am running through the standard test in order to identify the source of the problems.
One of the tests i did was changing the connections of the Firewire (FW) card of my PC and also changing the FW ports of my MR816CSX. To my surprise i noticed that i there is apparently no sound when i use the port #1 of the interface. The device is identified and there seems to be a stable connection but no sound…
I was under the impression that both ports should work equally. Am i mistaken? Is there anything else i need to consider when i switch the FW ports?

Thanks for your comments!