I'm not really into headphones anymore either,
but, I just recently sold my Sennheiser HD600's (open) and I use a pair of Audio-Technica
ATH-M50x (closed) for walking. So I do have a little experience.
Your Senns and Beyerdamics were both closed-back so if you like that extra bass punch and isolation, my first advice is don't buy open-back headphones. Every speaker, even the ones you put on your head, has trade-offs. The 600's were so clear it was like plugging the cable directly into my brain... but bass lacked impact, and unless you're alone you get the dreaded "
can you turn that down?"
since everyone around you can hear what you're hearing.
The M50x's let me play as loud or as low as I please. They still sound good, but not
Sennheiser good. If they ever die I'm going to try a pair of AT's
ATH-WS1100iS headphones. Not that the 50's lack for bass, but I like trying new things when the need arises.
They aren't the best sounding cans in the world, but Koss PRO-4AA are loud, powerful, and indestructible. back in the late 90's I had a pair and I abused them in ways you wouldn't believe (had them connected to the SPEAKER terminals of my receiver... apartment neighbors and people outside the window could hear the music when they weren't on my head). They would not die.
Those are a few suggestions based on personal experience. I don't think you need to spend anywhere near $300 to be happy with headphones, much less double that. For me personally, that's the diminishing returns point, where spending more is either for specific features or for incremental SQ increases you may or may not hear. My top piece of advice is buy from somewhere that offers hassle free returns so you can buy-and-try. Amazon's partnership with Kohl's kicks ass for me because I live less than 3 miles from a Kohl's and can return anything hassle-free, 7 days a week.
And also... prepare to spend a huge chunk of your life on
r/headphones if you want a million opinions from a million people.
As far as your amp goes, well... if that's what blew your other headphones it's safe to say it's up to the task.