aggregate device with two interfaces?

What is the "it" that seems to want you to choose one or the other? Logic? Or Audio MIDI Setup? Or something else?

Yeah, logic only lets you select one interface at a time. Use audio midi set-up to create an aggregate device. This will make the 2 Onyxes into one virtual interface which logic can deal with. It will appear in the audio preferences of logic.

The fact that he mentions "aggregate device" in his post title made me think he is aware of the possibility, so I assumed something else was the matter. But here's how to create an aggdev:
http://support.apple.com/kb/HT1215

Sorry, I don't understand that. They don't appear "as a split"?

So only one is displayed? How about *System Profiler* (hold Alt, choose *About this Mac* ) ? Does it list two Onyxes under Firewire ?

In the Audio/MIDI setup utility. It's in the utilities folder in the apps folder.

Audio MIDI Setup has a little "+" sign in the audio devices window.

If you're on 10.5, have you tried clicking on the word "Help" in the menu bar at the top of the screen when you've got Audio MIDI Setup open? It's a menu! Type "aggregate" into the little text field for some magic.

Regarding the Firewire issue, there have been at least three threads within the past week covering daisy-chaining issues (or rather, the lack thereof) in depth, one of which with a rather lengthy contribution by the guy who ought to be awfully busy writing code for the Metric Halo series of interfaces but spent twenty minutes writing up a long technical explanation for info the thread starter could have gleaned from thirty seconds of googling.

Regarding clocking: What does the Onyx user manual have to say on the subject?

Message was edited by: spheric