if you do have a music server/Mac/pc in your audio room, the best interface is i2s which nobody uses. I use Ethernet with cat7 cables since my dac has a network card built in, IMO, the only way to go.
I use I2S and many of my customers do also. Most of my products have I2S outputs and inputs. The problem with I2S is the lack of galvanic isolation and expensive cables, otherwise I love it because it does not get reclocked in most DAC’s. My S/PDIF is just as good BTW.
I agree with you on Ethernet. It’s the only way to go. There are still hoops to jump through to get great SQ however, like:
1) AQVOX or SOtM switch
2) CAT8 cables, Wire-World Platinum
3) Ethernet cable isolator, EMO EN-70e
If you do all of these, it will make a huge difference.
Steve N.
Empirical Audio