Subway USB

[mongo]

And is it possible to get a sound card via USB?

No.

[mongo]

yes there is usb sound cards for  example x-fi

http://www.amazon.co.uk/dp/B003RRY3WE/ref=asc_df_B003RRY3WE2944771?smid=A3FQIEOFZOU5HP&tag=googlecouk06-21&linkCode=asn&creative=22218&creativeASIN=B003RRY3WE

But obivously someone would have to make a driver for amiga os

Yes, there are USB sound cards. They will not work on a Subway because the Subway does not support isochronous transfers which the USB audio class requires.

[mongo]

this is an amiga sound card http://www.vesalia.de/e_delfina.htm

And your point is?