Software changes the sound much more than one would think. If you really want to hear how much of a difference it can make try out Jplay. I'd avoid Jriver like the plague; not only do they say that software does not make a difference(if that's true what is the point of their software
, a bit contradictory) but their program does some nasty things to your computer if you have it installed and try running a competitor's product. You might want to read some of the stuff here: http://jplay.eu/forum/jplay/jriver-install-message-httpjriver.comjplay.html/
After un-installing Jriver I had to reinstall a few programs that it had uninstalled on me or corrupted including my graphics drivers.
You might also find such differences between even the standard Windows media player, Media Monkey, and Foobar if you don't want to bother with free trials and programs that cost money.
Likewise you might want to try some of the audio PC tweaks on sites such as computer audiophile. I'm curious but what are the specs of your PC and Mac? I did an interesting test with Jplay a few weeks ago where I compared the sound of my desktop PC(with music on an SSD vs. mechanical drive) as well as controlling my PC through an ultrabook. Despite what they recommend on their forum I found the best sound having my desktop work alone with the solid state drive. Whenever the laptop or mechanical drive were used the sound became muddy and bright. Digital audio is fussy like that; it seems simple on the surface but in all honesty it's much easier to get a turntable setup than it is a good digital playback system on your PC.