You would have the option of using a digital connection to used the DAC in the headphones, or use an adapter to use your old headphones.
This is not directed at you, so please don't take it that way. I have been getting very frustrated with Apple as of late:
<Rant mode on>
In addition to the options you have pointed out, I also have the option of going with a different phone and computer ecosystem. My wife and I have had iPhones since the first one was released. We also have been using macs since 2006 after switching from the Windoze world.
The DAC in the iPhone is actually excellent, but don't take my word for it: Just go take a look at the headfi forums. Most if not all users on this forum will never be able to hear the difference between any modern DACs in a double blind test.
Considering the current assumed trajectory of App$e, my family is sadly starting to look alternatives considering the fashionista direction of the company.
Case in point, when you consider that all of the devices we use headphones with and that have 3.5/1/4" connections with in our home:
We have three receivers, a 2500.00 professional DAC, a 1000 watt PA, guitar/phone interfaces, 5 computers, and our cars all use 3.5" jacks for universal COMPATIBILITY . That is just off the top of my head, we probably have more. Count how much money those devices might cost together. 50-100k depending on the price tag of the cars.
Now here comes Apple with a 800.00 phone that requires a proprietary connector... Now all of these devices are going license and add a lightening connector because Apple says the connector is old? Yeah right!
Oh so I can buy an adapter for 19.99!
Adapters do have one universal rule, they get lost easily and usually at the worst possible moment. I outright refuse to buy a dozen or more proprietary adapters from App$e just so they can pretend that they are moving the world forward from a technology that has nothing wrong with it.
I don't boast, but for the sake of this rant, I have been on about a dozen published CDs and many more recordings, many of which have been mixed in or recorded in my home studio. I have a very experienced and trained ear.
In my studio I can currently listen to and record 24 bit/192 Khz music with the crappiest 3.5" headphones with the right music sources and DAC. That is right, you bring me the worst but working analog headphones, and I will play 24 bit/192 khz music through them. Amazing isn't it????!!!! They won't sound anywhere as good as my $600.00 Beyer Dynamics, but they WILL play any bitrate of music available.
Anyone who knows anything about digital audio reproduction knows that going to "digital" headphones is mostly snake-oil when it comes to delivering the best possible audio reproduction. The lightening connector and moving the logical location of the DAC and amplifier will not magically make headphones better, but will in fact shrink the possible use cases for higher end users like myself and make us gallop to the competition. Oh and the competition knows this btw.
It has been a good run with Apple, but I am probably getting off the train at the next stop (Yeah go ahead and tell me good riddance, I don't care. I have music to enjoy and use cases that App$e apparently no longer cares about. I will gladly take my money else ware).
You know what is an older connector than the 3.5" jack? Yeah the three prong electrical outlet. Apple, it's time to ditch those old fashioned outlets. You should come up with a new safer and convenient design that requires us to replace our old fashioned electrical outlets. Oh and you can sell them to us at 79.00 a piece. I know there are a lot of people on this board who will gladly rewire their entire houses for you, then buy adapters for their old fashioned lamps, appliances, and other electricity consuming devices and laugh at me for my old fashioned 3 prongers.
</Rant>
