Thoughts on DAC option

Your DAC seems solid, I would not change it to try and solve this problem. Do you notice a difference when streaming from the PC vs. the Mini? In both cases, what type of connection are you using to connect to the DAC?

Speaker performance and interaction with room acoustics have by far the biggest impact on sound quality. You might want to consider getting a measurement microphone and putting the REW program on a laptop. Then run a frequency sweep and review the results. You may be surprised as to how uneven the response is. That can be addressed with acoustic room treatments, adjusting speaker placement, and/or adding room correction.  I added room correction to my system and got an improvement in SQ that was well beyond any equipment change I've made. 

There have been many good suggestions so far. In addition, I would experiment with the filter options on the Vega. When I owned one years ago, they definitely could impact the sound. This will not make huge changes, but it's free.

You might benefit from a EQ in the system to take down the top end of the Krix by 2-5 dB when you are playing rock. In looking at the graphs in Australian hi-fi, the response, though smoother and flatter than most, does rise by a few dB between 1 kHz and 10 kHz. This definitely could manifest as sounding "harsh" on many current recordings. 

If I were you, and, because your speakers and components seem quite satisfactory, I'd start with doing some experimenting with your cabling.  Cables can make or break any quality audio system.  Happy listening.       

Vega has a pretty decent DAC section and built-in analog preamp designed to minimize distortion and noise. So I agree with all the gentlemen suggesting you leave the Vega as is and focus on the cabling instead. Refining cables to tune the sound is a great approach—it works in my system, though it does cost money. Speaking from my own experience, if someone as frugal as I am doesn’t mind spending on cables, nothing should stop you.

When it comes to interconnect cables, DH Labs and Cardas are two affordable brands worth considering. In general, DH Labs’ silver-plated series offers more dynamics and punch in the low end, while Cardas’ pure copper provides a smoother presentation. Both feature gas injection to vacuum the line, reducing dielectric constant and capacitance that sort of good stuff.  The choice ultimately comes down to personal taste. Beyond their price point, the law of diminishing returns kicks in—and it’s up to you to decide whether you want to go further down that rabbit hole.