so i did a few testings, like you guys suggested.

i'm on a mac btw ;)

playback testing

1. i tested a dts-cd wav in vlc (latest version) and it plays fine through system speakers

2. the same dts-cd wav in vlc through toslink was a no go. the system settings simply switched the output device for an unknown reason

3. muxed the dts-cd wav to .mka and then vlc played it just fine through toslink and my amplifer saw it as dts and playback was fine

4. same mka file in mplayerx gave me white noise - could be because of an older version i'm using, as the newer version gave me serious playback problems on some movies

digital capture testing

1. i cannot change the gain level when i plug in my optical cable. adobe audition would always jump back to 0db

2. multiple capture of the same file - 3 to be precise and they all looked the same. there was no change in the waveforms hight or what not...

conclusion

i guess the mac is doing bit-perfect capture and output (if used in certain container formats like .mkv/.mka). maybe i try to get myself an external capture device. would the M-Audio Firewire 1814 a good choice?