I got my fx101s finally yesterday. I have them burning in right now, but i must say they are VERY nice.
The bass is simply insane. I'm not a basshead but the bass is just mindwarping. My first thought was that someone had stuck a sub woofer in my ear. They're almost the polar opposites of the fx40s which are extremely quick, high-end detailed, crisp/sharp, and separated.
These 101s are smooth, punchy, and warm. At this point (2 hours burn) the bass is a little overwhelming - not the balanced sound of the 40s. But that's not criticism, that's the nature of this beast. The bass is extremely detailed, textured, and extended beyond anything I've ever heard. What's more, it isn't at the complete expense of the highs like the she3580 can be, they have tons of body but also represent the other qualities of the music. Almost zero breath in sound stage from what i'd listened to, but some noticeable depth. 40's have these beat in that arena thus far.
On some tracks, the 40s sound almost too fast and crisp - where the 101s have wonderful decay.
Dsnuts, i can now understand why you said we should buy both. They compliment each other so well. Its quite a shame really, as i find myself in the position of again wanting the best of two opposites in one set of headphones.
Not to mention that the fx101 is much easier to listen to than the fx40; while the 101 is much punchier in impact and quantity, I can at least listen to them without cringing ever few seconds and ripping them out of my ears.
I'm now curious as to how they'll sound with burn in. I actually noticed with the little burn in i had, that everything else had started to come through the awesome bass. Vocals are just about right, and the snares and cymbals were a tad distant in some songs, which is a great deal better than sibilant and painful. But holy cow, the bass is fantastic.
Anything by phoenix sounds fantastic, and i'm just blown away by the floor bass in "obsolete" by MuteMath, and the jazzy Melody Gardot's voice sounds warm, rich, and smooth.
I'll admit, not being a basshead (yet, at least) these probably don't fit my criteria of ideal sound at the moment (although this might change). However they are definitely an experience I would not pass up, for the $17 i spent on them i'm extremely happy. I'm not exactly sure how they'll burn in, but i can definitely say that they're going to get a ton of mileage as my pocket/casual phones and be recommended to friends.