if you heard the mini3, the uha4 sounds almost the same as the mini3. aggresive.
I haven't, unfortunately. To be honest I haven't tried many amps at all, apart from RSA and Pico amps. I usually just try out iems and headphones when I have the time.
I currently use a C2 with my dt1350s by the way, which doesn't have a line-out. I have read however than the headphone out is very clean, which is why I'm still open to buying amps to really drive the dt1350s.
I really love their sound. My friend bought the hd25-iis as portables, so we compared them. IMO the neutral, well-extended sound of the dt1350 is better for me, though I am sure many would prefer the hd25 for the "fun" sound. I would say the dt1350 is for a very intimate experience with the music, while the hd25 is for toe-tapping fun with the music.