People always say that anc headphone sound bad when wired and power off and I agreed until I try them power off with a preamp with headphone amp , in my case the Fosi P3 tube preamp.
The sound separation is way better, the sound doesn't get distorted at all specially the bass and the sound in way more relaxed and light to the ear!
I want to know the technical reason of why this happen. It is it because when you feed amp signal to the headphones and the headphones are on the headphones amp that signal again and the drivers cannot handle that very well?
I would like to assume that because when off you have to boost the bass on the preamp and it also allow you to get more volume without getting distorted. The sound loses a bit of body, is different, but I like it way more. Without preamp/amp I would not use them power off.
I don't know about 1000xm5's, but I totally agree using my 1000xm3's wired. I think they even sound better wired and then turned on.