The M15 is absolutely fantastic but I've found that when you listen with a lightning cable anything above 90% volume will have some background hissing, however this issue doesn't happen when using USB-C and so when using another device you can take the M15 to full volume. With M15 it's always a compromise powering it with an iPhone/lightning cable combo and so the on the go experience isn't as good. With the CMA18, there is no such portability compromise and the bass is just gloriously punchy. I have both the LCD-X and LCD-5; both sound incredible, but the M15 is incapable of realizing the full potential of the LCD-5. The bass punches with the CMA18. Hands down best portable audio experience I've ever had; it is unreal how good these sound. I would wager that when the reviews start to land that the consensus is going to be that CMA18 is the best mobile DAC ever made.