Which DAC did you use this with, or did you only try it with the iPhone 3 line-out?
If you don't like the mids and so on, it could be because Miu-tech selected AD8620 / NE5532 for that specific sound, or weak synergy with your headphone or IEM.
I thought it was a pretty interesting choice by them, but I removed the NE5532 fairly quickly.
A really easy solution to lower the hiss and RFI is to exchange the positions of NE5532 and LME49720 with one another.
I'll try playing with it.