24 bit files...

...is iTunes downsampling to 16bit when you import them ? (check import settings).

I presume the APE connection to the CA DM is via Optical ?

Lastly - how do you know they are only playing at 16bit ? the CA Dac Magic only shows the incoming sample rate in kHz.

PS: The USB connection on the DM is limited to 16bit, 48kHz...no matter what the incoming file is being played at on the streaming device.

Hope that helps you track down the issue...which I doubt is with the DacMagic.

If I remember correctly, others have reported that the Apple Airport Express (AAE) only supports streaming up to a max of 16/44.1, so hi-res files are reduced by iTunes to CD-quality before sending to the AAE. iTunes itself will support hi-res, so if you have a digital-out on your computer and are able to plug it directly into your DAC, you can benefit from the better resolution...just not via wifi.

Cheers guys, iTunes is importing fine, bitrate is in the region 4600kbs, and yes AE to the DM is via optical.

I have just read elsewhere that the AE will only stream 16/44 so i guess thats the issue. Sadly it's a fairly old laptop with no dig-out so my hi-res days may have to wait!