I wouldn't think that audio data would suffer too much from TRS cable I/O interface to Aux I/P. I have noticed that pk-pk voltage O/P is a bit low for home audio amp 50 k Ohm 'ish I/P impedance and thus vol can be a bit low.
The biggest question is the sound system's overall fidelity to take advantage of hi-res audio data. Getting good fidelity all the way out to the air from the speakers is not and never has been cheap.
I can say that I have been using an emulator device to play digital files to factory headunit in a MBZ Bose system in W140 sedan. It was a late 90's high end system and the Grom emulator decodes up to 24 bit/48kHz flac files so I use eac3to to downsample hi-res non-DRM files to play thru the Grom unit.
The sound is incredible! The clarity is great. The dynamics with the 24 bit depth to the digital data is the biggest change over CD quality; more so than sample rate of 49kHz vs 96 or 192. I am going to order a cable to use the Pono directly just for curiosity, but the convenience of using the headunit U/I playing from USB sticks is pretty convenient.
I can't say enough about how good the sound is though, but the Bose system in the car has about 14 speakers, a big power amp to drive them and double paned glass to make the car quiet, etc. It only took 15 years after manufacture to finally get audio data to make the system sing.
