to my ears at least, I used the m15's on both of the earphones at the time and comply foam tips on the u6t.

I had issues with fitment on the silicone tips, but you can tell straight away that its a 64 audio iem, the targets are identical.

The Bass on the u6t had surprising had a good amount of quantity, i was honestly super surprised by this. the U6t decayed quicker than the a4s.

The A4s definitely has bass force, that the u6t didn't have. The mids where a little bit more present of the u6t, or they sounded closer on the stage, where as on the a4s its more relaxed.

The treble sounded similar to me, but its definitely elevated on both.

All and all they are both very good IEMs, I think the u6t is definitely more balanced, abit elevated bass, while the a4s is bit more fun.

The funnest of the bunch I tried was the Trio, its bass response is elevated and the female vocals are a bit closer on the stage(compared to the a4s), that iem really put a smile on my face.