Are you able to confirm that it is as simple as running a jumper from the PT8211's DIN to a spare pin on the Teensy 4.1, then altering the sketch?
You can't just choose any spare pin. Only certain pins can transmit digital audio.
The pin functions are documented in 2 places. First is the pinout card, which comes with Teensy 4.1 and can also be found on the Teensy 4.1 product page, and also this page.
https://www.pjrc.com/teensy/pinout.html
The digital audio pins are shows in yellow.
While this serves as reference material, the compact format doesn't really communicate the finer details of exactly how you can really use these pins. For that sort of detail, you need the 2nd main documentation source.
The audio design tool is where the audio library software features are documented.
https://www.pjrc.com/teensy/gui/
If you haven't used the design tool, this 31 page tutorial is a good place to start. There's also a walkthrough video which closely follows the 31 pages of content, if you prefer watching a demo.
https://www.pjrc.com/store/audio_tutorial_kit.html
You might skip to part 2 which begins on page 8, if you just need to learn how to use the design tool.
As you click on each item in the left side, you'll see its documentation appear on the right hand side. All of the input and output features have a "Hardware" section which explains which pins are used.
As a practical matter, if you will connect 2 different audio chips, you will need to create a design using this tool which the software features that communicate with those chips. So before you buy parts, before you start connecting wires, use this tool to make your plan.
When you drag the various features onto the canvas, if you put 2 or more onto your design which can't work together due to a hardware resource conflict, you will see little yellow error triangles appear. A message with a (probably terse) explanation of the conflict might appear too. The point is this can help you to immediately know whether you have chosen outputs which can work together, and you can see the documentation about which pins each uses. That documentation panel offers quite a lot of other info too, which can really help you. Best to read it carefully.