Headphones and Hearing Loss

That's very helpful. I was actually considering a pair of momentum for myself. For my father, maybe these will work well too.

He'll be listening mostly to CDs on computer (no serious audiophile set up). Classical stuff, primarily. I've heard a few on audiogon saying they weren't crazy about Sennheiser, but it sounds like they may be perfect. I'll try to demo some this week to get an idea.

Sennheisers are wonderful. I had HD580 (same drivers as HD600). Very comfy with great highs and midrange (last thing you need are bass heavy headphones) but high impedance (300ohm) made it difficult to drive to very high levels. It was also open back.

I agree with Kijanki. Sennheisers are so nice to listen too and so comfortable. I only own AKG K702's and would NOT recommend them for your father. I do however have a son with the Sennheiser 650 I believe to be the model. They are fantastic.

Why not get custom fit, inner ear headphones?

I own the AKG 701 the Sennheiser HD 700 and one that may be just the ticket the Bayerdynamic DT 770 pro, which are available in several impedances. They are an over the ear and closed back model. The 770s are not their top model, you may want to read about a few of your potential choices on Hedfi.org