I conducted a test which compared playing an LP, and listening to the same LP on PC playback. The PC play back was a clear winner, it was equivalent to a cartridge upgrade. I attribute this to my rebuilt vinyl computer interface.
After buying a new interface, I removed and replaced all of the capacitors with superior caps; this would be the same as having a superior phono pre between you and the computer.
If you're not getting the same results, don't blame it on the computer.