I have the iPhone old SE for this purpose, my old iPod is still good, however, the iOS version 9.3.5 may be not support lossless .... I can only prove it with the coming RME .....
Unfortunately the first gen iPhone SE seems to max out at 48kHz with Apple Music, even if you enable higher resolution streaming. (It properly supports 44.1kHz and 48kHz switching with the RME though, but no higher.) At least that's my experience with my first gen iPhone SE. I haven't seen this limitation documented anywhere by Apple, so it's possible there's something wrong with my setup (maybe it wants more buffer space and I'm pretty short on storage). But perhaps they made this choice because the hardware is getting too old and slow to work well when streaming higher sample rates.