So, the W2 came in, and surprise twist, it actually has significantly louder transmission of EMI. A/B'd with an S1, both set to similar volume levels (by listening not by displayed numbers), both on low gain with a Fiio LC4.4B cable attached to a pair of FH5. I also tested with the W2's lightning cable as well as the Meenova one off Amazon. It is also definitely the cell radio on the 12 Pro that does it. I would turn off Wi-Fi, on the W2 I could hear it right away, on the S1 almost none if any (both with something playing and without). Then run a speedtest and the W2's noise was quite loud, and the S1 was pretty slight (again both with something playing and without). I then repeated the tests with cellular off and Wi-Fi on, and they were both fairly quiet.
I also noted that the noise was reduced on both by outstretching the USB cable, instead of stacking it behind the phone. Additionally, the noise changed a ton by moving just the balanced headphone cable to different spots around the phone, which makes me think most of the noise is either post amp somehow, or it's actually coming into the DAC/amp areas through that port, not the USB like I first thought. I'm really supper new to this sort of stuff, so just some educated went to college for engineering guesses.
I also agree with jwbrent, I only really started noticing this when I moved to a balanced cable (just don't really want to be pushing and pulling MMCXs a ton trying to A/B that).
I also noted the S1 kind of feels better made. The case feels thicker, it's a bit heavier, and the round metal buttons feel much better than the W2's sharp squared off ones (they almost feel like plastic on the W2).
I honestly couldn't tell the difference between sound on both, and the FH5 clearly don't need the extra power. That with the price, and the better build, guess that means the S1 is sticking around and it's actually the W2 going back. And then if the noise bothers me the cellular goes off while listening (not like a DAP would have cellular anyways)
Super not scientific by any means, but just wanted to get an update out there from my experience with them both in case someone was hoping the W2 would solve all their EMI issues for double the price.