It has a line output, what is it that makes it a no"true line output" ?

@LajostheHun thanks for asking.  You're right, it does have a line output to Speakers.  Unfortunately when you use this lineout with another amp to bypass the DX1's amp section, you end up with a situation where the volume control on the DX1 remains operational while connected to another amp section, unlike say the DACmini.   Hope this clears a few things up.