Using my collected headphones as Dayerdymanic DT770-80, TD770-32, DT880, DT990, Audiotechnica M50x's blue and standard , Austrian Audio Hi-X15, Sony MDR 7506 I decided to rty to build my own headphone Monitor.
Pre-build shell have no any plastic parts- real wood and steel used here. As speakers I decided to use AKG 371 replacement speakers, but heavily modify them.
As Headphone AMP I use my A1-inspired AMP with high -end parameters.
As result I have my own build monitor headhpones sounds very nice and transparent..;-)