According to what I have read about BT is the music is streamed in a compressed format. Some of the stream data is lost during transmission. This will definitely affect the quality of sound coming out of the device. That being said, if the MDR 1000x is aptX compatible and your phone has a qualcomm processor in it (many android phones do, iphones not so much), it will provide practically lossless streaming to the headphones. But it MUST have aptX processors on BOTH sides. With all that being said, AUX is wired connection and lossless by default. Its disadvantage is that you are now "tethered" to your device.