DSD DAC/Headphone amp for iPhone?

I have Sennheiser HD800 and Beyerdynamic Amiron headphones. What is your recommendation for the best combo DSD/DAC headphone amp out there? I want use my iPhone X as my hi res DSD playback device using the currently installed Onkyo HF Player app that plays DSD ( .DFF and .DSF) files.
Is there such a plug and play Portable converter amp? If so what’s the cat’s meow? Money no object.
It must be truly portable. Ie. Battery powered/chargeable.
Thanks!