Already answered by others, but a few comments.
Remember that my primary goal was not mobility, but replacing my headphone system with “the best”. (Limited) mobility was just an extra benefit.
In order of increasing sound quality (and decreasing mobility), you can connect headphones to an iOS device in many ways:
Bluetooth, compressed (including the vaunted AptX). AirPads are in this category, I think.
Wired headphones driven by the iPhone/IPad built-in DAC and amp, pretty bad
Lightning cable/DAC/amp dongle, like the Audeze Cipher, that goes through the Apple software. I have two of these, the closed EL-8 which I bought for air travel and now use occasionally when I don’t want to disturb my wife because all my other cans are open-back, and the iSine 20 which I bought as an experiment, don’t like how they feel on my ears but use for exercising. The Audeze headphones are excellent. Sound quality is limited by the Apple software to 48k, and the dongle has limited capabilities, but overall they are very good and warmly recommended.
A USB DAC connected with a Lightning adapter but powered from the iThing. Limited by the small power available. For example, Dragonfly is highly regarded, I haven’t tried it myself.
A USB DAC connected with a Lightning adapter with its own power, either battery or from the wall (wall power of course limits mobility). That’s what I now use for my top end system, with the Hugo 2.
Each level has its use.
(Btw, I also wanted to upgrade my headphones at the same time. My Audeze LCD-3 are excellent, but they are pretty old, technology has advanced. They are also demanding to drive. The Hugo 2 could probably have driven them, but I got the new Audeze LCD-4z which are easier to drive.)
Why pay £700 for a phone and strap that on it making it useless as a phone. If want decent portable audio buy a dedicated player instead and keep the phone for being a phone.
Isn’t that obvious? It’s in the title, because of simplification! On a more serious note to use a phone as a phone these days it’s a blasphemy I believe.
Uh, because it plays my entire Roon library, both local and Tidal, without requiring separate content management such as fitting 2 TB of music into 256 GB of storage? Because it is always up to date? Because it supports Roon’s user interface, so I can find an album by any contributing artist or composer or title or tag? Because it supports DSP?
Remember, my purpose in the OP was not mobility for travel or running, but for disconnecting me from cables around the house and backyard.
For travel I do have a player. It’s a hassle and annoying, but I need to, until we get remote Roon.
I have and use this combo with the Blk micro ifi.(MQA rendering).
Stream Tidal MQA and Roon dsd 256 with 250,000 local trks including almost 2 tb of dsd to my headphones.
Not sure I understand: you are using the iFi and an iOS device as a Roon endpoint? That’s the same setup I did, with the iFi instead of the Hugo? That makes perfect sense to me. The iFi devices seem very nice (I have not tried one).
Or are you doing something else?
If so, please describe it.
Correct.
The ios/iphone is the end point on my network and sees my roon library using the apple camera kit.
The ifi uses its own high level dac and battery (won’t drain iphone battery) and
Yes, there are a lot of interesting trade offs possible for a true, walkabout mobile version. Find Tidal equivalents, store my library in the cloud, cache mode, automatic resolution decimation… We have discussed it at length, and the Roon team indicates they are on it, but it is nontrivial.
My somplificitation project was different, just within my own WiFi range, and no compromises — on the contrary, I was looking for an improvement on my home system. And all versions of Beethoven’s ninth and Kind of Blue.
In photography circles they speak of Gear Acquisition Syndrome.
Somebody pointed out that we can get off the GAS train because each of us has a better camera than Henri Cartier-Bresson.
I think there is an equivalent for us. It’s already awesome.
On a more serious note 
, who talks …
