I like a bit of high quality music myself, having started with it way, way back in the days before download and streaming music, when it was on this weird shiny disc like thing. I’ve got a small(ish) but much loved collection so far and I’ll keep adding to it.
However I don't agree at all that high quality source material is unsuitable for an iPhone, I've been listening to mine on my iPhone for quite some time. While it's clearly much better on good quality home audio equipment (what isn't?) that you can't argue with. With the right app on iOS it’s certainly possible to play most any format and high quality source material definitely makes a difference. Quite a big difference if you're using good headphones as well.
Out of curiosity, I just did a transfer of one of my albums, which is just under 1GB in size. 983MB to be exact.
My first transfer was using iTunes File Transfer to the Onkyo HF Player app, using a standard Lightning cable connected to a USB 3 port. The transfer time was 69 seconds in total, not too bad, certainly bearable. And it matched what I expected from years of transferring audio this way.
The second transfer was to a class 10 Samsung SD card, plugged directly into the SD reader on my iMac. Surprisingly (very, very surprisingly) the time for that transfer, using the same album, was 2min 34sec. I expected it to be a lot faster than that. Thinking there must obviously be some sort of error in the process I tried with different cards from different manufacturers and at different speeds. Different connections and adapters and finally a flash drive connected directly to the USB 3 Port, which turned out to be the fastest of the (non-Lightning) transfers at just under 2 minutes, but still slower than Lightning.
Honestly, I can’t explain the speeds, at least one of the cards or the flash drive I really expected to be significantly faster than the iTunes transfer, but no joy. I'm truly baffled and I just can't explain why the transfers weren't faster than they were.
To put my mind at rest and rule out some sort of issue with my iMac, I transferred the same album to one of my USB 3 Hard Drives (a 4TB Seagate) and thankfully that restored my faith in the computer and the technology as the transfer to that drive took just 5 seconds (if only everything was that quick.)
So long story short, I honestly don't see using an iPhone for HD audio to be an issue. I’ve been doing just that for a few years now, I think I started back with the iPhone 5 and that only had 64GB of storage, iirc.
When it comes to storage I genuinely don’t see the lack of external storage to be an issue. When we now have the option of up to 256GB of internal storage and most of our photos, files and normal music is stored in the cloud, just how much internal space do we need. Or more appropriately, how many HD albums do we really need on a device at once? You could comfortably have up to 150 albums, or more, and still have plenty of available storage on your iPhone.
So the storage isn't an issue, the ability to play the files isn't an issue, the ability to purchase high quality source material isn't an issue, the quality of the sound produced isn't an issue (provided you are using good quality cans.) So all in all, if you want to listen to high quality music on an iPhone, there's literally nothing to stop you.
(Waffled on a bit much, my apologies, as often is the case, I'm medicated to high heaven. Nerve damage is a bugger, but the morphine and other pills do make you awfy chatty. We're lucky. I could probably go on for a few more pages worth on this topic

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CD? What on earth are you talking about man? Is that some sort of slang for Creaky old Digital music or something?