worlds best headphones Sennheiser Orpheus ?

I believe those are no longer made...

Stax Omega II would be right up there, I'd think.

Cary CAD300SEI + Senn. HD600/650 is a pretty good combo too.

-Ed

I've heard (just the talk, not the 'phones) that the Sennheiser 650 is rather astonishing....

The world's best? You could definitely make that argument.
I've tried many other mid to high end headphone systems. None better the Orpheus. The headphones are a work of art, beautiful in both looks and performance. The amp also is a quality piece, although, I must admit, it does look like a retro high end German toaster.

You might want to ask over at http://www.head-fi.org/. The Orpheus is rumored to still be available under the right conditions from Sennheiser. It is an amazing looking piece of gear, sort of like an altar. Heh, at least I saw God when I looked at pictures. Depending on your tastes an Omega 2 with a Blue Hawaii is rather amazing and probably in the same league if you like electrostatics. The Sony R-10 is also a great headphone and rounding out the trimuverate of the top cans would probably be the HP-1000 series driven with the proper amplification.