Would the sound from the Sennheiser HD25-1 II be improved if used with the FiiO E7 portable amp?
That depends on what you have the HD25-1 II plugged into right now.
I'd be using a Cowon J3 and a HP Envy 14 portable computer as audio sources.
E5/6/7 will be a downgrade from the J3's internal amp (yes, it's that good). It may be a small upgrade for your laptop, however.
Very informative. Thanks so much for your reply.