I definitely like the AKG K501, and would love to hear a comparison with the HD650 for classical and jazz. The K501 seems to sound good from any amp that has a decent amount of power, but I miss a bit of bass body and sub-bass presence with them, even on some classical recordings, especially contemporary recordings that have really deep and rich bass.
I'm thinking that I might be more interested in the 650 over a T1 or he560 at this point, because I have a Lehmann BCL and I think these other two are not as good with that amp, which doesn't have a ton of power (which the HE560 needs), and is voiced to have tight bass and detailed/emphasized highs (which may make the T1 sound harsh). The amp is good enough that I would rather get suitable headphones than spend a lot on cans and then have to get another amp.
Also, do people still recable the 650 to get a bit more of a punchy sound, or has that fad passed?