the way it works... source->box->avr->tv+ home theater speakers.
Q5ii is very old, can't do a lot of things, incl playback of 4k, 10bit, hdr, has problems with some DDtruehd tracks, some subtitles.
still, for a 7-8 yr old box, it is still blardy good for playing back 1080p, incl BDMVs, dtshdma - this is rare for such an old box.

now that u have new 4k hdr tv, u should get q10pro.
it will play anything u feed it with.
BUT... your avr of home theater is old... Q10pro will set it at max 1080p and dts/dd only.
4k, hdr, hd audio will be downgraded to what the avr can handle, i.e. u will not get the best video/audio.
now, since avr can only do dd/dts, u have nothing to lose by connecting q10pro->tv via hdmi, then tv audio digital output toslink/coaxial->avr.
this way, yr tv will do 4k hdr but audio will be just dd... and dd+/dts if tv has the capability.

get new box first, then get new AVR/home theater.

coaxial, optical are SPDIF - limited to DD, DTS; digital but not HD - cannot do ddtruehd, dtshdma, ddatmos, dtsx.

those, u must use hdmi + capable AVR.