I just bought my first set of headphones, the Hifiman He400SE and also ordered the qudelix 5k dac/amp.
Since i am very new to the hobby, i am wondering if the topping dx3 pro+ with more power would be a better choice for the headphone?
Only if you want to play impressively loud (above 110dB SPL peak so > 95-100dB average). You can make it play a bit louder by buying a balanced cable for the HE400SE.The DX 3pro+ can play a bit louder (using the stock cable) than Qudelix 5k in balanced mode (with new to buy balanced cable)
DX3 pro+ does not have the onboard EQ options and won't sound any better but has a display and is a lot bigger in size.
Qudelix 5k is small, portable (runs on internal battery) has EQ options and can add a microphone for taking calls on your HE400SE, at least when it is not too far from your head....
Totally different use cases for both devices.