Best bang for the buck in terms of sound quality is probably the Hifiman HE400SE, which is less than $100, the AKG K701 and Sennheiser HD6XX, which are about $200. The catch is that you need a proper setup to drive them. But to be honest, getting the tuning you like that suits the music is more important.
I’m sure it’s driving issue, 650/6XX’s treble is supposed to be smooth and veiled. I wouldn’t consider the HD6 series at all if you only have an unbalanced setup, the difference on my DAC is night and day.
