Foobar with WASAPI sound will not be good at all, try using UD-501 ASIO. and agree WAV does sound better than FLAC. Win 8.1 64bit will also make the sound more dynamic. However, can only do so much with Foobar, it isnt the ideal play back software, try JRiver with Jplay. Foobar tend to sound brighter and thin.
USB cables does matter very much, but you got to take care of the power in your PC first, the regular USB port from motherboard wont be any good no matter what cable you got.