Yea! I'm always impressed when I put this setup to my ear. For me it's definitely an endgame.
But I wonder if the M9 would have better performance with some sony DAP, like the zx507 for example
Oh yes the M9 sounds heavenly with the Sony NW WM1ZM2 DAP. Soundstage is really holographic, with excellent layering and instrument separation. Buttery smooth and organic and natural sounding, yet mixing showcasing the good technicalities that the M9 is capable of. Literal eargasm.
Unfortunately, the WM1ZM2 is almost 4K USD (I auditioned it for 30 min at the shop but couldn't afford it). The Questlye M15 is multiples cheaper, but as per usual in this hobby, diminishing returns hit hard the deeper you go down the rabbithole.