why not spend the money and get a streamer.
Your phone is not the ideal server nor a basis for an audiophile set up. It wont stream Tidal decently I've tried with mine, fine for low rez head phone work but not ideal for a home system.
You'd be better buying an older mac mini with an optical out.
Something like the oppo server an all in one item that checks all your box's and has an amp built in. also apple airplay and tidal. it will also act as a preamp so get some good powered speakers and/or and headphone amp and your set.
there are many others ranging in price also many that have more features.
With no disrespect to the above contributors, Apple TV, AirPlay, the iphone DAC and Chromecast are not audiophile solutions. Many would also agree that a Mac Mini is also far from ideal as a steamer. For top quality you need a dedicated streamer and a DAC/amp. I use an iPhone 7 and stream Tidal via Auralic Aries but you can also look at Auralic Aries mini. With no budget listed it’s very tricky to reccomend a DAC and headphone amp. For mid market prices look at the Chord range (hugo/mojo/hugo desktop). If you are looking for a small portable headphone set up with IPhone then the Dragonfly Black or Red.
The digital outputs of the Apple Airport Express or Apple TV and of the Chromecast Audio are bitperfect, and hence have no sonic signature. That would come from the DAC that one uses. An external DAC may improve the sound, but the inbuilt DAC of these devices is actually pretty good. The question here seems to be how portable the system has to be.
I use an iPhone 6 (or iPad Air) in this configuration with great results:
iPhone 6 ➟ Apple Lightning to USB 3.0 Adapter ➟ UpTone Audio USB REGEN ➟ dB Audio Labs Tranquility DAC ➟ etc.
The DAC in the iPhone is bypassed with the Adapter. The REGEN does its re-clocking thing and, to my ears, contributes quite a bit to the equation. IMO the resulting sound quality would satisfy many audiophiles.
With virtually no budget limitations the OP is in an enviable position. Separates? Tubes? Balanced? Space constraints?
I like the Chord Mojo DAC/amp. Reasonably affordable and top notch sound with headphones or even as DAC input to a high end system using a decent quality y-connector. I use mine with Iphone and IPAD (Apple lightening adapter required) as source with various headphones and as DAC into my full size hifi setup.
You guys are all way off in your methodologies.
There are a ton of great amp/dac/streamers.
The op has mentioned headphones that doesnt mean the Op dosent have or will have a set of speakers in the future or has a set now.
Also Tidal is important but with Tidal built into the device doesnt mean you have the phone streaming to the device the phone acts as a remote control for the device.
Also useability isnt being discussed.
Products by Naim have a fantastic app and allow all types of streaming to allow for youtube via airplay or android via chromcast plus built in headphone amp, also allows direct blue tooth streamIng.
Naim uniti atom covers all bases.
Also Roon integration isnt being mentioned.
Nor is Mqa.
Nor is how important is sound quality which level of Audize.
Also budget to some people even when they say is open isnt really, many newbies dont really know pricing and what it can go up to.
For example a cary dms 500 streamer is $5000 plus $1500 Cary headphone amp plus cable would be great is $7000 what the op will spend or is $3000 for an Naim Atom or something cheaper really desirable.
You have to ask the right questions nobody mentioned portability is a factor either.
Dave and Troy
Audio Doctor NJ
All good suggestions here. The Ayre Codex with balanced output is also an excellent option. I use the Ayre Codex in my own personal headphone setup as a DAC/AMP. The Chord Mojo or Hugo are also both good options as well. I’m also using a raspberry pi 3 via WIFI to stream Tidal to the Ayre Codex DAC with pretty good results. I use the Lumin app on my iPhone to control Tidal. The Raspberry Pi is surprisingly good for $35 dollars. I used to use the Apple lightening camera adaptor but I stopped because I didn’t like my phone being tied up in the source chain. I rather use the iPhone or ipad as a music streamer controller. I recently purchase the Sparky USBridge (allo.com) for about $180, which as a built in jitter reclock, so the performance should be pretty good. If you have the money to spent...you won't go wrong with the Ayre QX5/20 streamer/DAC. Good luck!
The Ayre comments were good but I don't think the OP wants to build a Rasberry PI device.
So the questions the OP should ask himself are:
1: How good do I want it to be which will affect budget?
2: Headphones only or a system with an amplifier for future speakers?
3: Is the size and complexity of the setup an issue?
4: Do I want the convience of having an app?
5: Do I require of possibly like the ability to stream other sources than Tidal to the system?
6: Is Roon or MQA something I know about or care to maybe play with?
7: Is portability something that matters?
8: Which Audize headphones are going to be used?
Dave and Troy
Audio Doctor NJ
I understand that toslink offers noise isolation and, if bit-perfect, it should be comparable with other streamers.
Check out this article on Chromecast as a streamer.
DAR is an experinced audio journalist and reviewer and I believe one of the best sources for independent information on digital audio.
For two years I used a Chromecast Audio (digital out via toslink) and was very happy to use it for Spotify Connect but the Aries is my go to source for better SQ.
FyI The Aries recently had a software upgrade and has Spotify Connect and so my Chromecast is no longer in use.
Thanks for the link. I read the Darko piece, but note (not for the first time) that he presents no hard evidence for what on theoretical grounds is a pretty implausible argument. I honestly do not think he is someone to take very seriously. Anyway, that is my take. See here for what I think is a far more solid review: http://archimago.blogspot.nl/2016/02/measurements-google-chromecast-audio_27.html
I am very pleased with my Pro-Ject Dock Box S Digital. Manufacturer's website: http://box-designs.com/main.php?prod=dockboxsdigital. It is a discontinued product, but as of January 2018 Amazon still had a few at $199.00 US. The internal DAC is very good and the sound quality is noticeably superior to the iPhone 7's internal DAC or a bluetooth connection. The included remote is somewhat useful. Nice feature is that the phone charges while docked.
I bought mine a few years ago to replace an Arcam rDock-uni (which sounded even better), Unfortunately, I fried the Arcam by connecting it to the wrong DC adapter (DOH!) and repairing it was going to cost almost $300.
I use mine connected to an Exposure 2010S integrated AMP, B&W 705 "bookshelf" speakers, and a B&W ASW 700 subwoofer.
How about a Marantz HD-AMP1 Integrated Amp/DAC.
Use the USB for a direct connection to you iPhone, or add an Airport Express with a Toslink cable to go wireless into your Amp/DAC.
Includes headphone amp as well as 35w/ch for some small speakers.
As an aside, I don't think the iPhone 7 has an internal DAC - no headphone jack at all. It uses a tiny external headphone dongle which I believe includes a DAC?