Thanks for reply. It's true, I misunderstood who you were.
Without any problems, I am using the same output hardware and option settings on an ASrock BeeBox (a NUC-like machine), running Windows 10, as I am on the Pi. They both are clients of an MC server running on a Mac Mini. Still, you seem to know whereof you speak, so I'm thinking you're right about configuration issues.
I'll take you advice and post on the Linux forum.
If the hardware works with windows, but not with the Pi, then it's either configuration problem or a generic Linux driver support problem; MC on Linux doesn't have any special limitations with respect to hi res PCM that I'm aware of. I'll weigh in with some testing advice once you get your thread set up.
BTW - as far as running headless goes, i have used an HDMI dongle to fake out software into believing a monitor was attached. i haven't used it on a Pi, yet, but if it works i believe it would be preferable to any (no matter how well engineered) software kludge.
If you're referring to the headless operation instructions above, you may not appreciate fully what those instructions "do for you." The purpose of those instructions isn't just to "fake out the software," they also give you a method to remotely configure and control MC on the headless pi without plugging a monitor or keyboard into the pi. You can use Gizmo or JRemote to control day to day playback, but neither of those tools allow for configuration, updating, or library maintenance (or even turning the pi off safely if you need to!). You need a way to interact with the actual desktop of the Pi once in a while, and most folks don't want to haul a monitor and keyboard over to the box.
Also, if you're not a regular Linux user, you may not be aware that VNC-server virtual displays aren't a "kludge"; they're a very common way to administer hardware that doesn't have a monitor attached, or, in the case of real servers, hardware that doesn't even have a display adapter of any kind to "fool" to begin with. VNC is a mature, long-in-use set of software tools.
An "HDMI Doctor" style dongle wouldn't provide any remote administration options, and isn't really necessary on Linux in any case: if you don't care about remote administration there are ways to force the XServer to start without a monitor attached, but I didn't outline them above because they're not particularly useful (you wouldn't be able to interact with it at all without plugging in a monitor). There's also no guarantee that such a dongle would work particularly well with Linux at step one, whereas the VNC solution has been extensively tested.
So I would advise against using such a dongle on the Pi, but if you try it, I would be interested to hear how such a dongle works with Linux (just out of curiosity).