Headphone amp and headphones... ?

Headphones, like speakers, are a very subjective, individual type decision. If you can, go to some dealers that have headphones and try them out and see what you like. It's the only way.

I've said it before, let me say it again. Buy a used pair of Stax electrostatics with it's dedicated driver unit. I
heartily recommend the tube driver units. For $1500 you can
find a pair on Audiogon. You will never regret it. The Stax phones create an ambient space and it sounds like you are there. Avoid the magazine hype that the dynamic phones
can sound just as good-they can't. No, I'm not selling a pair, I'm just trying to save you a lot of trial and error.

Stax certainly have a unique sound, but they are definitely not for everyone. You should certainly listen before you buy if possible. I agree that headphones can be very subjective and also add very distinctive from each other. The only problem suggesting dealers is that there are not many who put any kind of emphasis on headphones at all. Dealers like 32 Ohm in Portland are the exception to the rule, but I can't say I know any other (brick and mortar dealer) like them. You might check to see if there are any headphone meets in your area. Head-Fi has a "meet" section of the forums where meets are listed as threads, and or you could inquire about meets in your area. You might be able to hear some very thoughtfully assembled systems at a meet and narrow down some of your options further.

wish I still had my old Stax headphones... Grado's have nice tonal color but no where near the transparency of electrostatics. But oh how electrostatics will drill your ears if you don't have a sweet amp to drive them.

First - go to headfi.org to get the best feedback on this subject - its all they talk about and there are some very versed people on that site. There are also classifieds if you want to buy used.

Headphones are a great approach and one can far exceed the performance of an outloud system at a fraction of the cost/price. First thing you need to figure out is what type of sound you are looking for from the "cans". You may be best off hitting a store than sells a variety of brands and listening - at least getting an idea of which brands produce a sound that is most conducive to your tastes - then going to Headfi with that info for further suggestions.

What part of the country do you live? You should post that so others who have "phone" systems could allow you an audition of theirs - garnering you some experience for likes and dislikes and helping you get started in the right direction.