Audition won't play (S/PDIF, OSX)

Hey there.

I have this issue for some months now and tried to get around it several times but no solution turned out to work.

I have tried to reset all audio devices, reconfigured everything, reinstalled the OSX and also, this doesn't work with Audition CC either.

First, here's my specifications:

Mac Pro 5,1 (Mid 2010)

Intel High Definition Audio [S/PDIF used over ONKYO PR-SC5509, BOSE Acoustimass 15]

OSX 10.8.4

12 GB RAM / 3.2 Ghz (Quad) Xeon

Here's my audio-device settings (Audition):

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I'm quite confused about this, Windows' Audition plays audio fine (that is, independent of format: 44 khz, 48 khz and 96 khz work).

My channel map:

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Here's my audio device overview:

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Any chance fixing this? Thank you!