I've got a friend of mine who is purchasing my ATH-M50's and need a new pair of closed back headphones for work. I listen to a lot of rock, d&b, some rap, some classical. Very wide range of music. I have a Fiio E10K Olympus 2 DAC/Amp hooked up to my computer, so that's what I will be using it with. I have always loved my ATH-M50's, so the logical choice would be to just upgrade to the ATH-M50x, but I want to explore additional options as well. I've heard good things and am intrigued by the PSB M4U 1. How do these compare to the ATH-M50? Any other suggestions? Looking to spend ~$300 or less. That budget can stretch if it's worth the upgrade. Thanks in advance!