running a pair of headphones out of 'inferior quality' dac/amps, the components may not be resolving enough to pick up all the detail or may add coloration to the sound signature that shifts your focus away from certain characteristics of your headphone.
running the same pair of headphones out of a more 'transparent' dac/amp, the components no longer affects the sound quality as much, so you can hear the headphone's true sound signature and technical abilities.
this may may not always result in a positive experience. that is why some people spend a lot of different trying to match their external components to their headphones.
honestly, it may not even be directly related to 'portable component' vs 'desktop component.' rather it can just be that two different setups have different presentations & one is more preferable than the other. there is no rule that says desktop setups will always sound better than a portable setup. an example of what i am saying wld be a hd800 on a warmer-sounding portable device may sound better than a hd800 on a brighter desktop setup, considering how the hd800 is already tuned a bit bright.
basically, all the different experiences that ppl have had with their el8s can be affected by a lot of different factors and nothing that has been said so far sounds unreasonable (both the positive or negative stuff).
only thing posted on this thread that i wld be skeptical abt is mechanical burn-in for such a small driver size, but who knows. can't say either way unless someone does some real testing (measurements before & after of a few different el-8s at various 'burn-in' times)