Definitely works fine here.

What does 'undecoded' mean here and how it is going though my 5.1 speakers? Can Creative drivers for instance decode it correctly?

Btw do you have a sub-woofer channel output from the game in 5.1 mode or have to cut-off low frequencies from front channels?

i found something out
1. the sound settings is messed up
by choosing surround, the center speaker is not working ingame - changing to 6-channel fix this problem.

2. i changed soundmode=0 to soundmode=3 (il-2 best 3d modus)
sound is now changing when turning my head.

There seems to be a bit of a gremlin in the way the Config.ini/ memory managements works.
The Config.ini doesn't save until the sim is exited from.

Set the speaker selection, then re start the sim and the settings will take... if you just switch between speaker selection settings to test - yes, they mix up.

Similar thing happens with the Video settings