A dual core ATOM chip will do fine for audio unless you want to DSP or resampling on the fly. In that case you need the i5 or i7.
The downside to the NUC box is very limited expandability. For instance, if you want one of the upmarket USB cards designed for audio, you're out of luck, I think.
The PC in the link is also not fanless (active fan heatsink); the CAPS is.