My friend bought recently an m50x he has no dac amp, so I've gave him to try Fiio E10K to see if he needs it or not, after trying it he wanted to buy it off me as I've told him that I may upgrade in the near future. So I think it does improve the sound. As for btr5 I think it will suffice for m50x also try to get qudelix 5k it.s much better if you put the aesthetics aside.