Milli volt meter at the outputs of each device would be more accurate.I have both units, if i get some time this week I’ll hook them up via balanced inputs on my luxman integrated, play the same file played at the same time on repeat off the internal ssd, and see if i can hear a difference. I have a mic and software i can use to level match them, so I only have to switch inputs. Maybe will level match using the A6 as baseline and then adjust the A8 (I dunno, digital vs. analog volume??) I’m not sure I will be able to hear it… they both sound really good to me.
But we have the measurements of each, both are impeccable so there are probably other things you could be doing that might be more worthwhile.
Keith