Not saying its the answer but if you decide to go the analogue route, I'm running the Hippohifi Bloat (USB) which is sooooo easy to use and sounds good to me. Note: its 2 channels.
I would have liked to have gone with toslink but I run my DSP on a Zapco DC series amp which does not take optical inputs (shame, I wish the Bitone was out earlier).
You're running HAT, I just ordered a set of Legatia L6 mids, cant wait to install them!!!