there are majorly two types of all-in-one:
A - traditional USB DAC, added/attached medial player function, i.e mini-i (pro) 4, thus the medial player function has no UI control, no hardware remote control, fully depends on iPhone/android phone to operate the media player. in this case, the DAC is generally great on sound quality and normal DAC functions such as input switch.
B - medial player, added/attached DAC function, i.e. SMSL DP5, thus the medial player functions can be controlled by the unit more or less, as well as hardware remote controller; whereas the DAC function may buggy, i.e significant delay (>0.1 sec) and very complex to switch inputs.
Matrix mini series are traditional USB DAC, and as of Mini-i 3 Pro, it equips XMOS XU216 and femto-second clock – the famous Crystek CCHD-950. however, Mini-i 4 (pro) cut down all these hardware; and added the local file playback function as compensation.