x RELIC x
Headphoneus Supremus
I actually think the opposite. X5 and DX90 for example already has a powerful and excellent amp for a portable device. In what way an external amp superior to internal amp in a portable setup? Most people would use iems and sensitive phones.
I understand using an extenal amp for hard to drive cans but that application is for home and I would rather get a desktop amp instead of a portable one.
With X7 supporting modular amps stacking becomes more redundant and something a stack can never beat.
For my uses a portable amp prevents/helps me from purchasing a full sized amp for every room I want listen to music in with my full sized headphones. I have my special seat with my amp, but I'm not always listening there.