I'm currently listening to a Forte through AKG K701's, which seems to have a little difficulty driving. Currently the dial needs to be around 1/2 gain (-15 db) for a decent level, even higher (-8 db) for live jazz... this is with the power adapter plugged in.
I don't know if it's just new and the hardware needs to be "burned" in or if this is by design, but when switching between an old RME Fireface 800 headphone stage, I can say that the RME seems to have a slightly warmer and fuller sound, with improved focus, rhythm and dynamics, in some ways it just sounds "right". Also, the RME is able to drive the same headphones at 1/4 gain.
The character of the Forte, in comparison, is more forward and favors the mid to high frequencies over the lower spectrum. It also could be said to have a detailed, almost analytical sound which can, when combined with it's forward nature, overpower the more quiet portions of the sound-stage. Sometimes I can't put my finger on it but I could swear there are tendencies to be out of phase in comparisons with the RME, but that could be my interpretation.
Bottom line, when I currently listen to the Forte, I find myself focusing in on the sound detail, and when I switch to the RME, my foot begins to tap.
Then again, this could all change with proper burn-in time. 
I realize that the two interfaces are vastly different but I find it's always good to compare equipment from a reference point.
Although, with Focusrite's claim to create the "Best Sounding Interface" (they can make), I thought I should see if there is anything to this claim. While the specs are very impressive, it seems like those must a given these days... it's how it behaves within those specifications I'm more interested in. How are the dynamics? Sound-Stage / placement? Tone separation or saturation? Transient response?
The RME is a 10 in / 10 out interface compared to the Forte's 2 in / 4 out, so when you factor in the difference I/O, age and price, one would think that the sound should at least be on par... especially when you have interfaces out there like TC's Impact Twin at $400, which IMHO has a very good headphone stage, even compared to the DAC-1 (Benchmark).
I'm not trying to discourage people from the Forte, It has a significant amount of features going for it: it's size, USB/buss powering, MAC/PC compatibility, and it's quality of sound for the price and size. With that though, if size is not as mush an issue I would still recommend an Impact Twin if you're looking for a nice, clean headphone stage... it's also $200 less.
Anyway, hope this helps... 
Edited by ModernViking - 12/21/12 at 3:53am