This shows how difficult it is to design noise free digital mixed with analog circuits, hence why smartphones with audiophile-grade DACs alongside wifi/bluetooth/4G in them have not been taken seriously.
Perhaps the X7 with the hot-swappable amp module is another way to deal with this plus it gives the user customisable add-ons. I wonder if the DAP architecture can be made open so that third party companies can build/release their own version of the amp module/cradle to rival that of the *pod.
See how far the IBM PC went when it came with ISA expansion bus support for add-ons
The audio connection standard is quite well defined in professional application, if you work in a recording studio, stage, or even P.A. industry, the connection requirement are all well defined and they can tell you the pin definition, impedance, and level of different audio connections right away. Unfortunately when we go into HiFi industry, the standard are loosed enforced only.
Take non-balanced line out as an example, the standard RCA (or 3.5mm) line out should be 2V, however you probably have noticed that a lot of DAP line out are not meeting this standard.
The problem is the loudness war actually has extended to portable audio product market. For instance, when users connect their source to several amplifiers, very often they perceive the louder amplifier as better, more powerful, or more dynamic, so the easiest way out to win the game is to increase the gain of the amplifier. As a result of that, some manufacturer has increased the gain of their portable amplifier to a very high level, and this will let them stand out and impress their users (or potential customers),
I can recall when I was a consultant to Cayin during the N6 beta test stage, I have once advised Cayin to tune the line out of N6 to 2V, as this is the standard after all. Unfortunately this turn out to be a bad advise because when connect to a portable amplifier with very hign gain, N6 will sound harsh and over driven, and there are more High gain amplifiers then standard/low gain amplifiers in the market. At the end of the day, the line out of N6 was set to 1.7V and it works well with most portable amplifier so far.
So can we set a standard in DAP architecture for audio connection? Yes, you don't need a rocket scientist to do that, and we have the professional audio industry to look up to.
Can we rely on such a standard? Unlikely because the standard can hardly enforced strictly.
PS. I diverted the attention to audio standard because I cannot comment the architecture of a competitor product