[hdmkv]

Thanks looun... yes, FLAC is bitstreamed, and 192kHz is indeed passed (AVR front panel shows this).

Subs look indeed good on both players and that's very odd.
Since I have owned a Q5, I know for sure it was not working then.
Stupid question.. but are you sure that those subs aren't hart-coded...

That would mean I'd have re-encoded my rips , so nope. Above sub examples are from 1:1 rips in ISO. Only thing I do with all my rips, whether ISO or MKV, is mux only the necessary sub track in. It's the same English PGS track in the full ISO.

are Q10 and Q10 Pro based on the same chip?

Q10 Pro uses HiSilicon's latest Hi3798C V200 SoC, while current-gen uses Hi3798C. V200 is 64-bit, has HiSilicon 2.0 "Imprex" PQ engine, and supports 4K+HDR. It's also noticeably (though not significantly so) faster, including supporting higher bitrate clips. I've tested up to 255Mbps Jellyfish clips (H.264 & HEVC) w/o stutter, same as with nVidia Shield TV.

Do you have any filters enabled on your TV? like Smooth Screen or any of that "soap opera" effect crap?

No.