Have to chime in on the B52 here. This amp completely changed my point of view on tubes in head amps. Apart from the shameless price, it's been hard for me to find fault with, even though the honeymoon is over. Perhaps the only thing negative I could say is that it's better with higher-Z phones...

If you can stretch to two 9V batteries, a second hand Headroom Micro is a good choice - particularly with the desktop electronics module. Bit fiddly to change the batteries, but you get used to it, and it has a lot of muscle and sounds great with most portable phones. ( Only the older Micro's...

Another vote for the HD650. I have a choice of phones (not unusual on this forum :-), and find myself always returning to my 650's for classical. I enjoy their balance and coherence with massed, complex music. I can listen for hours, and not feel tired. There are more exciting headphones, but...

I regularly drive my HD650's with my Headroom Micro with desktop module, and am pretty happy with the bass. It's somewhat tighter and more articulate when running on external power supply, but on battery it's still by my call very good. This is my standard config for listening in hotel rooms...

My first set went 6 years, then developed the dreaded dandruff. I don't notice any sound degradation as they age - my call would be to leave them till they start to crumble. Peter