So a few initial thoughts, and will add more after a few days, as I find AK usually takes that amount of time to stabilize sonically.
Firstly, a little disappointed that the initial sealed unit had a channel mis-wiring, Left was right and Right was left. Luckily Jaben Hong Kong had another sealed unit and was kind enough to exchange and open another fresh unit for me, after I checked it was not my player, to test.
Great service, and a huge thumb's up to them.
OK to the combo 380CU and CU amp. It is worth it and adds very nicely to listening with than just the player. Better control all round. I will listen a few more days before adding more thoughts about the combination. I prefer listening to the combination with the amp set at high gain, finding it sounding richer, fuller with better fluidity and density in it's presentation.
Most of my time was comparing with Stock 380 and amp with my in-ears....and it would probably go...
380Cu/Cu amp > 380Cu > 380Cu/amp > 380/Cu amp > 380 = 380/amp
My 2 cents