I have a pair of m50x and since they sound pretty bad from my (android) phone I decided to get an amp/dac Fiio Btr1k. The fiio device can be used wired or wireless, but I don't know if I can use its dac function through bluetooth and I don't know if I can use it connected to my phone through usb while listening to spotify.So can you please inform me about the forementioned things.Also if I can't use an usb dac with spotify what other music players can you recommend me? Thanks in advance 
