Limitation ro 24/48 may be not the Apple"s fault...
Have you tried high res audio player on the iPhone such as ONKYO , and check what"s on when playing 24/192 files...
I think 24/192 is sent through the lightning output then... but you may need a real DAC to benefit from this High resolution.
CIPHER is merely an expensive microphone for using SINE to phone.
SINE audio quality deserves to connect it to DAC-AMPS such as MOJO or OPPO HA2.
I wonder this myself. But it seems that all of the devices that work with the high res iOS audio apps (and I have several, including ONKYO HF Player, TEAC HR Player, and my favorites KORG iAudioGate and NePLAYER as they explicitly show the output sample rate) ONLY send out above 48kHz when using an Apple lightning-to-USB adapter.
I have not yet found a set of lightning headphones which can receive anything above 48kHz across the lightning connector. The Audeze Cipher is an example (24-bit, 48kHz max). (Notice that Philips Fidelio are also advertised as "24-bit" but never mention sample rate.)
Another example are my Sony MDR-1ADAC, which when connected via USB to a PC support up to 24-bit at 192kHz PCM in hardware. With Sony's included Walkman cable, up to 192kHz PCM is supported. However, when connected via Sony's included lightning cable to an iOS device, only 16-bit at 44.1/48kHz are supported according to the manual. Although, in actuality, with iOS10 I can only get 16-bit at 44.1kHz (and not 48kHz, even with 48kHz sources).
The Apple Lightining Earpods will receive at 44.1kHz and 48kHz (don't know the bitdepth). Of course, these are very low quality earbuds, but interestingly the iPhone will correctly output the most appropriate sampling rate depending on the source (e.g. 192kHz is output at 48kHz, whereas 88.2kHz is output at 44.1kHz).
Overall, this all wreaks of iOS software limitations, not hardware limitations. Which means it should be fixable in software, if Apple would care.
My desire is to use the iPhone with headphones that contain an internal DAC/AMP and have it sent native sampling rates and bitdepths - I don't want to carry around an external DAC/AMP for travel. No reason why this shouldn't be possible, if Apple supported it - in fact, this is exactly what Audeze told me with regards to the Cipher.