Really sorry about the slow response – I’ve been away.
I’m also afraid I have no technical knowledge – I’m just a user, noyt a programmer. I know that picorep****r uses squeezelite too and could do passthrough (check out v 1.18b). As with hardware squeezeboxes it was initiated by setting output volume to 100%, but that’s simply an interface issue I guess.
Clearly passthrough of DTS-enocoded flac over HDMI is generally feasible as the kodi installation in max2play already does it. But it would be so cool if you could add it to your squeezelite implementation.