I tested my ak380 black with and without amp. The only thing i noticed is that the bass becoming a little more tighter, and somewhat the overall sound is getting a little brighter. I really don't get it why people always said to me with amp the sound is better. Better? or brighter? If they like the sound a little more brighter, then of course with amp is their choice. But what i really wanna say is that without amp, ak380 black is already suit my taste best. The most important part here, is the quality recording it self. Some recording it does sound warmer, and some of them is brighter, no matter what type of files they are (DSD, Flac24, WAV, Flac16). If the recording file i play is a little brighter (more open) then i do like the sound from AK380 alone, and if warmer, with amp should be nicer. My theory is that simple. And personally, i do prefer using AK380 alone without amp. (my amp its been in the drawer since the 1st day, i only tested couple times and i don't like the bulky looking)
Is AK380cu better? i will find out soon to prove how good they are. But one thing for sure, IMHO, on certain songs, i do believe it sounded better if we use regular/black ak380 (on certain IEM/CIEM/Headfon). The gear matching is also the most important part in the chain.