Depends on the BD player. I use 7.1 analog from my Oppo BDP-83, for DD/DTS 5.1 as well as TrueHD/DTS HD Master 7.1. The AQ is much superior than the S/PDIF coax connection. I have also noticed that the output signal voltage is higher on the analog 7.1 out than on the coax, since you can adjust the sound trim level coming out of the BDP. You should compare the two and see which one sounds better on your BD player.
