I will attempt to clarify a couple of points. That anything can stream music to Bartok by Bluetooth is incorrect as Bartok has no Bluetooth facility, nor do other dCS devices. You can, however, stream to it using an iphone or ipad using Apple airplay and, yes, you are right, the signal uses your LAN/WLAN. Apple airplay can stream audio from all sorts of sources ( not just Apple Music or i-tunes) installed on the ipad or iphone, I use it frequently to stream podcasts or other items from BBC Sounds to my Vivaldi just as I did dCS’ own fascinating podcasts about Mercury Living Presence. However I haven’t tried it with the Qobuz iOS player. I expect it would work albeit downsampling hi-res material.
When a codec is used such as AAC or MP3 although they are lossy the file/stream itself is still ( usually) 16/44.1 or 16/48 at replay. However although the file/stream capacity in terms of bit depth and sampling frequency remains the same as the uncompressed original the information that is contained within the file/stream is not complete. That which is considered inaudible by the codec promoters has been disposed of i.e. it is lossy. Mosaic reports the encoded file/stream it is receiving so e.g. Mosaic will show AAC 320kbits/sec but when Rossini DAC receives it after decoding by Mosaic it is 16/44.1. albeit with missing information compared to the original. So that is why a lossy file/stream is still displayed as 16/44.1 or 16/48.
For simplicity I would stick to using Mosaic for local file replay, Tidal, Qobuz, Deezer, Spotify and internet radio and leave the i-pad for items that are unavailable in the Mosaic suite of sources.
NB: Apple Music now supports lossless 16/44.1.