No they are not physicaly the same. First of all there are different driver types. Dynamic, planar, electrostatic are the most common (in that order). Also different materials of the mooving part, different thickness, different magnets, differently placed magnets, different driver size, different driver form. Then there is everything that surrounds the driver. Damping, back/lack there off, size within the headphone, driver angle, pad material etc.

There are ALOT of differences but yes the driver itself is verry different usualy. You cant EQ alot but if the drivef is slow or cant moove alot of air at once you will always have a muddy non-dynamic sound no matter what you do.

Please before buying anything expencive take the time to visit your local hifi shop and just find out for yourself by listening!

Amps make a big difference. Dacs can make one too but if you have a decend one I think they should be the last part of the chain to go crazy with.