Not so good with ER4S (Tralucent T1 is better for that) My T-Peos H-200 sound great with BH amp.
If you have DX50 and H-200 by all means I can easily recommend adding the little amp. Mainly because H-200/BH have already made crazy synergy recommendations in the main C&C BH thread so feeding the amp a clean signal like DX50 offers you instant win/win. Another IEM that goes well with BH amp is TF10, very good synergy there.
I could not recommend BH amp for ER4S lovers though, they're much better off with T1, for example.
Thanks! I love ER4S. I will consider T1 in the future.
Also, thanks for pointing me to T-Peos... I just found that I cannot buy them in Hong Kong.... interesting.....