Just finished an "upgrade" to my RPi3/Hifiberry Digi+ Pro/Volumnio streamer into my Yggy. I added a 75ohm BNC socket to the PCB (had to wait for 5 week delivery at a min ordering of 10, so I have plenty left) and had a custom BNC cable made (Canare BNC connectors with Canare HD-SDI cable) along with
@Baldr 's recommended Neutrik BNC -> AES converter. The result is very interesting.
Both RCA/BNC-BNC sounded a bit grainy. This really stood out when listening to violin pieces like
Theme from Schindler's List, or
Zigeunerweisen by Mutter. In comparison, the BNC > AES connection was really smooth and coherent, there is no break off when the violin is played on different strings (low vs high). The BNC->AES connection also deepened the bass a great deal, the drum beats in
Danzon No.2 is so much more enjoyable on the BNC/AES then either RCA/RCA or BNC/BNC.
I might just go for a 502DAC to try out if AES -> AES could do better magic.