From iOS Deezer app -> Airplay 2 -> Airport ExpressI have an iPhone 6s also. With recent Fw upgrades, Deezer's airplays show 44 on dac, instead of 48 as before.
So there is no reason why it shouldn't pass the lossless flow. Unluckily I ended my trial time before those enhancements. If I'm not wrong, the label "FLAC" was shown, despite the final airplay post upsampling.
Any test will be appreciated, at the moment I'm stuck with android but in the future I could change back and deezer could strike back, since I liked it's app.
MQA lights up for 2L MQA CD albums
This is not possible if the album was transcoded to 256kbps AAC on iOS...