Your Oppo has asynchronous USB, making PC hardware irrelevant (as long as driver is good). I can only guess, that computer injects electrical noise into Oppo. I would try USB cable without power wires (GND, +5V). You can also try different USB cables or add USB isolator. Plugging computer into different outlet might help. (in my home outlets are divided into two phases).
I don't know Foobar2000, but there might be gain adjustments, equalizers or upsamplers, that need to be turned off (eliminated). Another possibility is that your digital music file rip from CD was poor (error correction code approximates samples when CD is scratched or laser is dirty). Also make sure that you compare in exactly same conditions at the same time of the day (same amount of ambient electrical noise).
I don't know Foobar2000, but there might be gain adjustments, equalizers or upsamplers, that need to be turned off (eliminated). Another possibility is that your digital music file rip from CD was poor (error correction code approximates samples when CD is scratched or laser is dirty). Also make sure that you compare in exactly same conditions at the same time of the day (same amount of ambient electrical noise).