Help with multiple Audio interfaces

[LittleJJ]

Guys, I'm stumped (that said, I stump easily). I am trying to add physical inputs to my DP setup to accommodate new synths. I use the Apollo firewire interface and am trying to add a MOTU 828, sync'ed via word clock. Everything seems to be going OK until I get to Configure Hardware Driver and highlight (select) both the Apollo and the MOTU interface. Within about 10 seconds I get a spinning wheel of frustration and an error message: The audio hardware did not respond. (MotuAudioSystem Mas MasCoreAudioWork Thread.cpp, 99 [57:0]).
Then I'm done, because it takes me back to Configure Audio Driver and I must choose either the 828 of the Apollo butcannot do both. And whatever interface I choose, the other one goes offline so I'm getting exactly nowhere.
Can anyone tell me how to get this setup working?
DP 9.12, Mac Pro 12-core running Yosemite

[Don T]

Hello,
Create an aggregate device. you may also have to turn your host multiplier to 2.

[philbrown]

I'm using a FW Apollo with a USB Midas M32R > DP8 and it's working fine. Maybe these are set in software and this suggestion is moot, but I would look at the sample rate of the units and DP and make sure everything matches up. It may be that one is set at 44.1 and the other is 48K for example. Just an idea.

[rickorick]

Did you shift click on the second interface? That's how you get more units to work at the same time.

[HCMarkus]

If you are not using available optical i/o on both devices, consider connecting via optical ports and using the 828 as expander, not an interface.

[RodneySauer]

If you are not using available optical i/o on both devices, consider connecting via optical ports and using the 828 as expander, not an interface.

I'm using that technique to send 8 channels of digital audio from an older 828mkII to a new motu 8m, which then forwards it to my Mac on its thunderbolt cable. (There are ten channels on an 828, but the optical cable can only carry 8.)