There are two comments I would like to make.
(1) Look at online auctions. You will be able to buy something very much better second-hand.
(2) You write that you would "like to try a hybrid/tube amp for the supposed added warmth". I think this is a mistake. Never buy amplifiers that "add warmth" in significant quatities, these are not Hi Fi.
The K701/2s are beautiful neutral headphones. If the musicians perform warmly then you will hear in in the K701/2s. If the musicians perform coldly, then you will also hear it with the K701/2s.
If you have an amplifier that adds warmth then while this might be attractive initially, you will soon tire of it.
I do listen to classical music, but what I write holds true for any music form. Musicians work very hard on the tonality of their instruments, brilliant musicians using computer generated sound will attend to all aspects of the sound. So then if you amplify the signal through an amplifier which "adds warmth" you simply wipe out all that hard work. You will not hear the subtleties in tonality they have built into the music.
I write about computer generated sound, but also you can consider the violin. The brilliant violinist will manage to tonality of output, it is essential to their expression. If you use an amplifier with "adds warmth" once again you will be wiping out great quantities of the work the musician has put into that performance.
I have listened to Hi Fi since the 70s. I put together my first Hi Fi system in the late 70s in fact. All the main amplifiers designs can be good or bad depending on their implementation, however I have found that my favourite amplifiers always seem to be Class A Solid State amplifiers. I have heard excellent valve amplifiers (what in the US are called "Tube amplifiers), but the vast majority of valve amplifiers I have heard unfortunately are simply dosing on great quantities of even order harmonic distortion (that is the distortion that makes the warm sound).