I really like the separation between the bass, mids and highs, I iust feel like they're bass-light, whether they have 2 drivers bass dedicated or not. Maybe I just need to experiment with more ear tips? That is only my initial impression. I've only spent an hour or so with them so far.
Welcome to the club of happy Westone 4R user :-)
and also I'm using Fiio E12 as well combined with my Iphone 5 a my portable music gadget.
post your impressions here as soon as you got your Fiio E12.
as for the tips, I suggest to use the comply foam tips like Tx400 to get more bass effects http://www.complyfoam.com/products/tx-400/