After hours of flaming frustration that no one in the world makes
around-the-ear (aka "can") headsets for cell phones (I wear hearing
aids), I found that Sennheiser HMD 280 PRO cans (apparently) come with
no end connector, and you are expected to wire in whatever you want.
This sounds just fine by me, except that I don't know enough to be
able to tell if wiring up an end connector is all that is needed for
this to work well. i.e., impedences? capacitance? need an amplifier? I
would like it to work "great" since the headphones are gonna cost me a
lot.

Can anyone take a look at this and tell me? Any help would be greatly
appreciated!

I put the specs for the headset on my website. Please delete the 'X'
in "goldXfinches" after you copy the link.

Specifications:
http://goldXfinches.org/HMD280/Sennheis ... ations.gif

Headset wiring diagram (not too exciting):
http://goldXfinches.org/HMD280/Sennheis ... Wiring.gif

Sennheiser page for the headset:
http://www.sennheiser.com/sennheiser/ic ... s_dj_04976

They also make an HMD 281 PRO which is the same thing, but with a
different impedence.