Looking for my first DAC

A few months ago I bought a Pro-Ject Pre Box S2 Digital DAC for my office system and have been extremely happy with it. Stereophile just released their 2019 list of recommended components and the Pro-Ject DAC was included in their A+ list. At $399 it is the only DAC listed at less than $2,000 and the prices in that group range up to $30,000.
Crutchfield, for one, offers a 60-day no-questions-asked return.
https://www.project-audio.com/en/product/pre-box-s2-digital/

I agree you could mod the OPPO and that might serve you well for awhile but think there are some good reasons for a separate DAC. 

Transports in disc players fail, they always do eventually. My experience has been that as player models change so do the transports inside them and it's sometimes impossible to find a replacement for a model that's no longer current. Without a working transport the DAC inside may be useless, no matter how good it is.
  
And my experience is that most of the advancement in audio quality over the last few years has come from the improvement in DACs. You could reasonably argue that speakers and amps have improved, as well, but the degree of improvement in DACs seems to me to be greatest. I expect that will continue.
 
And, an external DAC gives you more flexibility as new sources of music come along.

@curiousjim -- The Project-ject Pre Box DAC replaced a Simaudio 100D, which I'd always been happy with but, as happens often, I was curious about the latest changes in DAC technology.

The improvement was substantial, better soundstage and a more 'articulate' sound while still sounding sweet. I was impressed with some of the little touches. As an example, the output level can be controlled from the front panel and the level for output to the integrated amp needs to be higher than the output to the Sennheiser headphones. Once you've set both levels on first use it remembers them, when you plug in the phones it automatically switches levels.

But the thing that impressed most was the improvement in the sound. I like it much more than I expected to, which hasn't always been the case when I get new gear. I think it's the best bang for buck purchase I've made in 50 years of swapping gear.