The er4s' came in, listened to a few tracks. I like! Tonally the first thing to come to mind was hd800, which I find to be somewhat lean but I didn't think the er4s as being bright on first listen. I did get a nice seal and the bass albeit somewhat lighter than my shure se535 was quick tight and punchy. Treble is fantastic, very smooth, no etch. The level of detail was pretty impressive, again great retrieval and didn't sound bright to me.
Driving with a pico power, these things like their juice! Medium gain with iPhone headphone out on full, I was close to 11 I clock. The pairing sounded great.