Where/How can I further improve PC audio quality?

I just started listening to streaming PC audio. The app I'm using is Spotify and the audio card I installed is an Evny 24HF outputting 20 bit, 96khz. I am using a 280 fiber glass Toslink connected to my Cambridge Audio AZURE 840C which upsamples to 24/386. Overall, it sounds pretty good, however I would really welcome feedback on how I may be able to improve audio quality. I am using Spotify Premium and selected high resolution and hardware excelleration. Thanks for your help!!
The solution I'm going to try is a better card that has only digital outputs and claims to support asynch for improved clocking and a claimed low jitter output.

Just out of curiousity, what card are you going to get?
Short story is, everything matters with PC audio. The cable quality, electrical noise within the PC, PC power supply pollution, yada yada.

MP3s will never sound good, upsampling does nothing for them, and upsampling any file type/quality is not a guaranteed improvement.

USB works well, it's what I use, but often an external signal improvement device (reclocker, etc.) makes a world of difference. 

I built a custom PC server, all custom "audiophile" parts. Expensive. Then spent another $2-3K on external signal improvement and it made a big difference. Feeding into a $4k DAC. And there's even more I could do.

So, it never stops, you are at the bottom of the ladder now and there is a lot that could be done to improve.
How can you improve PC audio? Get rid of the PC..........