The 660 SoC is pretty decent for a DAP, with 4xA53 and 4xA73 based cores, that can run @ 2.2 GHz max. I am even surprised that they were able to lay their hands on such a controller. For those that do not understand why I say that, I would recommend to read the posts from FiiO / James, for example about the screen and SoC of M15:
Both the screen and SoC of the M15 will be out of production by the end of the year , which mean no more M11 / M11 Pro / M15 after that ... And of course, no more support .
But you won't see any official communication by FiiO about this.