Grados sr60s are one of the most universally loved headphones here and for good reason. I'm not sure a guitar pre-amp will have the best sound quality and for the grados, you won't be needing it.
1001s are pretty nice too, but if you are looking for isolation, they don't do that too well despite being closed back, at least, from what I read.
Too bad you missed the blackfriday deal on the HD555.
Amazon is one of the best places to buy from in terms of cost though it varies from time to time.