I dont have the ER4S, but I can drive every pair of fullsize cans in my sig (except the K601, but that needs a desktop amp anyway) from the Classic using the T3, and its tiny. Whether you will get *everything* your ER4S are capable of is a question I cant answer - eagerly awaiting HPA's verdict on a couple of portables, and Skylab will probably have reviewed the T3 by January.
I had the Supermicro IV several years ago which was tiny - too tiny for most Line Out Docks. Qusp makes a really nice tiny dock and line out for small amps which I will be looking at soon. That one works with the Micro, but it harder to use with larger amps.
Get the shadow with a cable pro low profile lod and you will be in headphone heaven, I am also thinking of buying a pair of ER-4s to go with my set up, since the shadow was made mainly to go with IEMs. Has anyone heard this combination?