Have owned a DSJ since August and also was looking for best possible sound (within a “reasonable” budget). DSJ provides lots of input options. Some swear by I2S, some ethernet (Bridge), and some USB. Note that AES/EBU, coax spdif, and optical spdif are limited to 24/192 PCM. Which one works and sounds best is hardware dependent. Some servers have dedicated ethernet outputs, many have USB (another standard never intended for music), but very few have I2S (that typically requires a conversion box and additional cables).
Roon has become the music operating system industry standard due to its extensive metadata and seamless integration of Tidal favorites with locally stored music. From my research JRiver and Audirvana + are currently the popular (and less expensive) runners up.
Note that simple servers via ethernet may not sound any better than a PC via USB (that was my experience with i5 Small Green Computer/Roon/ethernet versus my general purpose MacBook Air/iTunes/10ft USB cable). Note also that sources are general recognized as being the smallest sound quality variable in the digital sound reproduction chain. Keep in mind that streaming is controlled from your PC, phone, and/or tablet but the actual sound comes from the router and that DSJ is not a wireless device.
Setting up and using a server can be daunting for the non-computer savvy. While thinking about all this, there are two other considerations. MQA is available on DSJ from Tidal and on some servers, with much debate as to sound quality. Content is limited, from my brief experience older recordings sound no different, but newer ones reveal more detail, especially in mid/treble frequencies. The other consideration is DSD (DSJ is limited to 256DSD) but realize that 99.9% of releases use lower format masters, so it’s mostly pointless.
Anyway after my trial with the Small Green Computer I’m back to using the MacBook until I find a significantly better sounding solution. Note that I listen in a dedicated room to a mid-field setup so the USB cable is not a problem for me (many really pooh-pooh a USB cable that long, but sounds fine to me and as mentioned, matched a dedicated/purpose built music server with “better” operating system and ethernet connection.