Can I can connect my Crown CP660 amp directly to my Auzentech Prelude (no receiver)?
Yes and no. Yes, you can do this but you do run the potential risk that you might get some loud sound you did not expect or whatever. The output is not as controlled as that of a receiver and thus there is a risk, however small, that you might get some undesired audio signal.
Beyond that you run into the problem that using the PC to control the volume means you are using a digital attenuation process which at some point can result in a significantly lower Signal to Noise Ratio (SNR). The problem is that you will most likely need to keep the volume down on the output and that is performed by scaling the digital values which reduces the output level of the signal from the DACs. The noise floor, however, is not touched. This means you will at some point hear DAC noise at low apparent volume levels. Not what is generally considered to be good thing, even with the relatively high quality DACs found on that card.
So you can do it but not without risk and not without a cost. In my opinion you are much better off to go with a traditional Pre/Pro.