The closed one is also great. It just has a slightly different sound, is less "airy", has more bass and is well insulated from the outside, whereas with the open one you can hear everything from the outside.

Headphone amplifier: for on the road or at home? If you want to connect anything else (instruments? Line in?), the Focusrite Scarlett are absolutely recommendable: https://www.digitec.ch/de....