The other earspeakers also improve with system improvements particularly the Koss ESP which benefit from amp/transformer upgrades. The stock system is lacking.
My Lambda Pros are a little bit light in bass impact but I still love them. The SR-007 is unimpressive with the SRM-007t but becomes a bass monster with the right amp and does wonders to vocals. I think the HE60 has enough impact for me but it doesn't have the syrupy thick bass that many people like.
The RS-1 is my favorite "normal" headphone, it doesn't need super fancy hardware just to sound good, so you can upgrade as much/little as you want.











