If you can cantrol the gain thru the computer then a power amp will work...
...if you've got one lying around doing nothing.
But, if you're purchasing either then I doubt there will be sufficient audiable improvement to justify a separate power amp over a receiver using a soundcard as the source.
IOW, there are quite a few entry level receivers that are more than up to the task which cost less than separate power amps, particularly if you want more than two channels of sound.