I upgraded from E7 to E17, and the sonic improvement is noticeable, even necessary for me as I was getting to know the limitations of the E7 too well. Flat (not fleshed out), subliminally a tad harsh (noticeable on my PFE 232 which have a bit of grain themselves), and bright in a way that I could not ameliorate fully with, say, iTunes EQ (due to the lack of liveliness and dimensionality of instruments). Detail is plentiful but a bit artificial, like a monitoring system but not like an audiophile system for long-term enjoyment.
The E17 is "not head and shoulders" above as someone wrote, but definitely shoulders. ;-) Well worth it.
I also sense a cleaner sound when using pure optical input with no charging (operate of battery). When I use USB input, I suspect some RFI comes in from the MacBook Pro and intermodulates such that the treble is a bit hashy. Small but there, more easily heard after spoiling myself on the optical connection for awhile. It affects the rest of the audioband I believe, just that the lower treble is most detectible to me.
My reference for comparison is my iPad 3 with Arrow 4G. The iPad lacks the deeper bass, but has good imaging and a graceful sound overall. The Arrow is not bright, and gives "dimensionality" and proper perspective among treble details, harmonics, dynamics -- a sense of realism hard to describe, but "head and shoulders" above the E17 even.... Still, the E17 is enjoyable, particularly if you have your "detail-seeking ears" on.