I own the S:flo2 and the Sony X, which I bought recently, and to me, they are both excellent (and I use them for different listening situations). On balance, I prefer the S:flo2 for at-home listening, especially with the T3 amp I just bought and high-quality mini to mini cable I own, although the HP out also sounds very good as well. For on the go, I use the X, because it has external controls, so I can use it "blind," something the S:flo2 doesn't allow because you must use the touchscreen for all but volume.
Right now, I have the DBA-02s, but I am considering the SM3s as my top tier IEMs and may buy them soon based on what I have been reading.
However, even as much as I like the Sony X, I have a Cowon J3 on order from Amazon, because I want an on the go player that also handles flac, which the J3 will do. It also has a card slot for expansion, which makes it more flexible. If the J3 even comes close to the X, I am going to sell the X here on HF and keep the J3. If the X is a clear SQ winner, I will just return the J3 (30 days return from Amazon).