I can point you out to some very excellent equivalents depending on your taste of sound flavor.. You like that big bold musical style of the FX850 but want to try Audio Technica's take on it. That would be the ATH-CKR10..Best vocal rendition in the industry as far as I am concerned and even a lusher bass if that is possible. Or if you want something more neutral with a silky engaging sound.. I highly recommend the ATH-M03 but with the cable upgrade AT offers.. I am loving the Nuforce Primo8 but the AT earphones offer a better value for the money for their given sound qualities.. If you don't mind spending a bit extra.. The Nuforce Primo 8 represents one of the best sounding 4 BAs. With the best isolation out of the bunch I suggested. You guys can read my thoughts on the Nuforce 8 on my signature or on the front page...I think it really comes down to ones own taste in sound to think any one of these earphones are "better" over the FX850.. Once you get to this level of sound performance all of them sound fantastic in their own way offering their own take on a particular flavor..
I like all of them equally to be honest. It really depends on my mood which phone gets ear time. Hard not to love the FX850 every time I hear them.