Of course it can be done...with a caviat:
The digital input port (SPDIF) can only carry 5.1 by means of Encoded Dolby Digital or DTS. This can cause one of two things to happen:
1: You can record the input just fine, but its in an encoded format
2: You can't record until the signal if first decoded (meaning you're recording software would need the relevent decoders).
I'm not sure which is the case, although I would assume 2 is the case in this circumstance...