Even the most expensive memory-based transport can usually be beat by a server, however I would not recommend using the S/PDIF or AES output directly from the server. Instead try a USB interface or converter with a very good master clock and design in the USB interface. I recommend using USB with a good 1.5m USB cable from the USB converter to the DAC. This was my go-to choice for many years.
However, the problem I have found with USB is that there are too many variables that affect SQ, even though I have now 6th generation USB interface on my own products. The cabling, the USB port, the power supply for the server, the playback S/W and AC power all have impact. For this reason, I decided to focus on Ethernet instead for the future.
Ethernet is not perfect either. Even though it is packet-based and does not rely on the audio stack in the computer and is fairly immune to the playback software, cabling and power supplies still seem to have an effect. However, the difference compared to USB is that: even with the cheapest cables and wall-warts for the router, Ethernet still sounds as good as the best USB. When the power and cabling are optimized, Ethernet actually pulls WAY ahead of the best USB IME. Simply the best SQ I have ever heard. Ethernet is not usually something you can drive with one of these servers. It's usually a computer running Jriver or the like.
If you must stay with the server, I would recommend to try a Berkeley USB converter because it is XMOS based and galvanically isolated.
Other things to consider:
1) format for best results should be .wav files
2) rip CD's with either DBPoweramp on Windows or XLD on Mac
3) You may be better off with a good S/PDIF cable rather than AES/EBU. AES requires higher voltage, which often leads to more stages and thus more jitter.
4) If you must use the feed directly from the server to your DAC, maybe consider a reclocker like the Synchro-Mesh in-between to reduce jitter
5) always use a good treatment like Utrabit platinum plus on the CD before you rip it
6) try a Plasmatron AC regulator from VHAudio - most manufacturers that have tried it swear by it as the best power for digital. I love mine.
BTW, I have heard the Vivaldi system in rooms next to my system at shows.
Steve N.
Empirical Audio
https://forum.audiogon.com/discussions/absolute-top-tier-dac-for-standard-res-redbook-cd?page=73