I recommend looking at this from the high level / sound quality perspective. Merits of the particular technologies… say R2R… etc. become irrelevant in the larger picture of the design of the component and each subcomponent chosen within the box… well, for that matter the box as well. So concentrate on the overall components.
If you want to assemble a good sounding system. Then you will want to concentrate on a streamer box and DAC to plug into your preamp. While there are many combined units, they severely limit flexibility in upgrading and generally do not sound as good as separate boxes (too much stuff crammed into a box). Since streamers are a bit newer than the DACs… it is hard to get the very best streamer and DAC in the same box at any given price level.
Choosing the right streamer / DAC will depend on the rest of your system. As I have built systems over the decades typically I end up with a system with each box very roughly of the same cost. You cannot make decisions based on cost… but very generally they reflect the amount of design effort, component cost, and assembly time. So, just generally. I bring this up, because folks tend to think that going cheap on the streamer is appropriate… it is not. It is every bit as important as the preamp or amp.
I have experience with components from the $500 to over $20K… more on the high end than the low end (see my virtual systems). But I can assure you that as you move up… say from the $1K component, doubling the investment repeatedly to over $20K there is a very profound and important improvement in the sound quality at each level (if you have done your homework and found the best for the price, compatible with your equipment and tastes). In general, all aspects of sound quality improve: transparency, tonal character, detail, noise floor, dynamics, imaging, rhythm and pace… etc.
I highly recommend looking at Aurender streamers… at the highest level you can afford (I own two). Each level up is a significant improvement in all aspects of sound over the lower. A very high quality DAC is required as well. I like Audio Research, and Berkeley… although there are a number of very good DACs for over $5K
Listening is the best way to evaluate, but this requires experience. DACs like other audio components are easily broke into hyper detailed vs natural / musical. Many folks want detail at any cost… the problem for me with that is they often remove the music and natural sound and they become sterile. Reading and listening, be cautious of reviews touting highly detailed / analytical or you can end up with a scientific instrument for extracting detail that does not make your foot tap and is without emotional connection.