For me, at the beginning they also sounded littlebit "muffled" and lacked in bass tightness & kick. After cable change and amping with at least 150-200h playtime, it "opened" up properly. Now bass&kick is tight. Also soundstage, separation and transparency much better. Totally in love with that sound they provide. The soundstage depth towards front-middle is just amazing.
Yes, they are warmish sounding cans with
only little emphasis on bass but FAR away from sub-woofer like basshead cans.
These cans are more meant for enjoying music while still being able to easily listen all the detail if wanted.
To make them sound better, they need exactly what Mike said in his headfonia review about them:
The 1840 is still more refined, and the mids and highs are smoother, but I find that a good tube amp can help the X1 in those departments.
This headphone has a good speed and attack by default, so I won’t be needing a solid state. What it needs, however is a little smoother treble and a little boost in the mids body. The ALO Pan Am is the best pairing I’ve heard with the X1 especially with the smooth Siemens tube upgrade.
And I agree with that... based on Aune T1 + Siemens E88CC and iBasso DX50. Both smoothen littlebit X1 treble and boost up mids section. Also bass is brought down tad, making them little more neutral. Result is very very enjoyable, at least for me