Got an update on the E8s and it's not good unfortunately; I've been using them for almost all of yesterday and today (around 10hrs each day with 30% charge left afterwards on Fri and 15% today so the battery life claims on the box are right!).
I noticed yesterday that the right earphone sounded a quieter than the left around 70% of the time, if I pause and resume it sometimes kicks back in and works normally. I got home today and actually sat down and tried to work out if I have a broken right ear or a broken right earphone and (fortunately?) it's the earphone.
I tried playing various tracks and then swapped the earphones around and the right earphone was still quieter than the left when I had it in my left ear. I also went into Settings on my phone and slid the slider thing in accessibility for adjusting output between the left/right channel and when I had the slider all the way to the left it sounded loud, and when I slid it back to the right it sounded quiet. I then played the same tracks on my AKG earphones and my Beoplay H9s and they both sounded perfectly balanced so it's not the music.
Will be taking them back to my dealer on Monday (will likely ask for a replacement - will mull on it over the rest of the weekend). Quite disappointed because they're otherwise fantastic 🙁