hello, i got a problem with 2 fireface400s:

they are set up as an aggregate device in the mac system and are synced via the optical spdif-connection and connected via firewire.

what happens is that they constantly seem to lose sync during the recording, resulting in 8-bit like distorted signals ( in the recording) in all of the channels that come in through the second (and synced as slave) FF400 (F29)

changing the drivers to the "built-in" and then back again to "aggregate-device" in logic fixes the problem for some time, but not for long (1-10 minutes)

has anyone expierenced the same / a similar problem with syncing two fireface devices?
are the sync settings of the two devices wrong?
the first device is bus powered, the second is powered via external adapter.

here's what the settings for the two devices look like:

i'm using them in logic9, mac osx 10.6.8, 2.4GHz Inter Core 2 Duo with the RME drivers and firmware updated (version 3.08 / v1.71)

maybe someone can help?
thanks!