I'm glad you got a good pairing. I found the er4s from ak100 lacked power...i used it also via my glacier amp and just found the ak100 too neutral for the er4s.
it worked v well with momentums.
I love etymotics myself. So i was disappointed. macbook pro to glacier to er4s is a great mobile setup, but unless I get a more coloured or relaxed amp/or same for new iems
I found the ak100 not to my taste.
What music are you using?