Hi- Welcome!

You might want to try posting this to the Computer Audio section for more comments on soundcards.

I'm not familiar with what's available in the area of high-end sound cards. I'm sure if you pay the big bucks you can do very well. But, my inclination would be to go with your first thought and run a digital out to your receiver. Many on this forum are very happy with Yamaha's on-board DAC's.

If you want more than that, my next suggestion would be to purchase a dedicated external DAC rather than an expensive sound card. You can buy them new or used. The advantages being 1) relative value and 2) moving the processing away from the electronically noisey enviroment inside the computer. But I would wait and see how you like the Yamaha first.

Finally, if you are using compressed files (MP3). You're biggest sonic improvements are going to come from using higher bitrates (<192mbps is very poor, some don't hear much difference at the 250 cut off) for encoding. Preferrably, use lossless compression formats. The encoding improvements will far outweigh the DAC improvements until you go lossless. Then you can start thinking DAC improvements.

my 2 cents.