Well, for me the DI-20 is a clear upgrade against the U16.
On the other hand, I've just tried on the DI-20 the HDMI I2S and the AES/EBU outputs. All the system remained the same during the test, just switching inputs on my R8 DAC with both cables connected. The cables used were a 2.1 HDMI 8K 0.3m long chinese cable (I think the one
@FredA recommended) and a fake chinese Nordost Odin XLR 1m long cable (wich I must say also sounds very nice as XLR).
Well, the AES/EBU input was a clear winner, as
@FredA and
@DACLadder anticipated. What I noticed the most was improved instrument separation and 3D pin point image. Bass was also better. Staying for now with the AES/EBU cable. Thank you for the advice!