Which apps on iPhone will apply HRTF to multichannel audio tracks for spatial headphone listening?

[triple_vee]

(guys, this is a cross post from AVS site)

On iPhone...

• Apple Music seems to support this in-app and transmit a binaural digital signal. Any ordinary DAC between Apple Music and headphones (wired or bluetooth) can decode this binaural digital signal. My understanding is that the Apple "supported" headphones that they call out (and try to sell ) are for the head tracking feature (a gimmick in my estimation).
• I have to believe that Amazon Unlimited and Tidal HiFi Plus do this in-app as well.

But for my ripped SACDs and Blu-Ray audio...

• Plex supports multichannel via ATV/Shield to my AVR and 5.1.4 system...not sure about HRTF on the Plex app on iPhone...maybe an external/portable DAC will work?
• Plexamp currently does not support multichannel much less HRTF. This surprised me that Plexamp (their dedicated music player) would be inferior to Plex with regards to multichannel music.
• Is there any iPhone app that exists to do this?
• Can I import my multichannel FLACs into Apple Music and piggy back off its internal support for binaural? Will Apple Music know to do this?

I would say the ecosystem for multichannel music is "ok" when playing through your home theater, but the results can be incredibly awesome. For me it was worth going down that rabbit hole. Now I'd like to have a reasonable solution for headphone listening to my SACD rips from my iPhone.