Use iMac speakers as center speaker?

Hi,

i'm considering migrating from PC to an iMac (late 2013) but i don't want to lose my 5.1 setup which i spent my life building.

I'm evaluating some alternatives and one of those is this one:

I own a yamaha amplifier with DTS/Dolby decoder. I'd like to use a TOSLINK cable to connect the iMac to the decoder in a 5.1 setup (i know this is working).

The output of the amplifier would be: Front Left, Front Rigth, Rear Left, Rear Right and Subwoofer.

I'd like to use the iMac built in speakers as the center channel (both of the iMac speakers, of course).

I know about the Audio MIDI Setup tool which allows a huge number of different connections between different sound interfaces.

I googled a lot before posting this discussion but all i could find were tutorial about aggreation of ANALOG outputs.

Is it possible to use the optical output for the surround (except center) and the built-in speakers for center channel?

I might consider building a statue to the one answering this 🙂