Received a 2nd hand E12 a few days ago and already I know it's here to stay!
Why do I like it with the X5?
Not because of the crossfeed (imo the SQ gets really awful with this option).
Not because of the +16dB gain. I don't have a headphone in the house that needs that much power. Even my LCD2 sounds pretty good without this gain at ± 60% of volume.
But...I really like what the (sub)bass switch does! The SQ gets fuller/richer and to my ears lots of music just sounds better with it when it's on. I don't consider myself being a bass-head, but maybe I should analyze myself again on this point sometime soon
I have a PicoPower also. When I compare the two, I think the PP surely has a cleaner and more neutral output, so it's more to the purists taste...but the E12 is the more ''fun'' sounding to me...
Btw, @ olddude:
There's a beautiful BLUE light on it!