I were choosing between this and ue trple fi 10 pro, and as for me ie8 is totally a winner.
Great bass, great detail, great everything. Sound is crappy out of the box, but in few hours it start to open up and in nearly 50 hours of burning in you are in heaven. Isolation and fit not super nice, but i made custom tips and now im as happy as one can be. I think it'll be my last IEM before IE9 or something like that. I really like senn sound sig.
UPD I forgot the widest soundstage you ever heared from iems. Its even wider than most over-ear headphones.