Headphone Amplifier. Which?

Question

Headphones

Bought some Marshall Major headphones. I liked it very much - a pleasant sound, but due to the fact that sometimes the music is directly from the computer, I want more. The Iphone starts to swing them at maximum volume, but they do not reveal their full potential, on the poppy the situation changes - at half the volume there is already enough volume and there are details in the music.
Can you tell me which headphone amplifier to buy? The criteria are the lack of installation of any software on the computer (I sometimes have music at work, but it’s impossible to install anything from the software on the working computer) and prices (I’m not a cool audiophile and the toad strangles more than 4k rubles).
I'm looking at Fiio products, but I just don't know which model to take.

Answer 1

Yes, I would like to put it in. But if it is mobile (with a battery), then I will not mind