According to Andrew Everard;
Apple AirPlay capability is also now handled in software, rather than via a separate chip.
(I think he’s smoking something funky 
)
IINM, Airplay on dCS has always been via firmware (on the Streaming Board), there’s no such thing as an Apple Airplay “chip”.
If I were to venture a guess, I’d say the Lina X likely uses a newer (different) Streaming board than the Lina (and V/R/B/NwB), and that newer board doesn’t yet have Airplay support on it’s firmware.
James mentioned Airplay support in the future with a firmware update;
The DAC X does not currently have AirPlay support, though we intend to add this in future via a firmware update.
ps: Can’t find detailed pix of the inside of the Lina X, could it be that it shares the same 1955 Streaming board as the Varese UI unit? 