I think i am gonna just throw my 2 cents on these iems, considering there's so few people frequent this thread (its probably just me at this point). Please note that I am no expert on audio so my opinion isn't solid. Also I picked the FXT200ltd
First of, the comfort: Unlike FXT90, I was actually struggling to find that sweet spot of comfort for these 200ltd. The right one just fit in fine, I dont need to move it around too much, but the left one on the other hand will hurt my ear if i dont put it in that perfect position. Even if i get it in the right place, moving my head around too much will dislocate it and cause my ear to ache. For the past 2 years i have never had any discomfort with my FXT90 thanks to its shallow fit, but that's probably just my ear.
- Isolation and microphonic: Because of the bass port on the back of housing, these phones don't isolate sound well, I would not recommend using them whille working out, commuting or using in loud enviroment. Microphonic is another issue, its not too severe but using the cable clip is recommended.
- Sound:
+ Bass: Coming from FXT90, when i first listened to these phones I was welcome by a wall of bass. Well, not exactly "wall of bass" but pretty sure the 200ltd has a somewhat thick, bodily characteristic. Its nowhere near basshead level however, I find it the about right for most of my albums, but on certain records it can be too much, causing the sound to be slightly muddied. I checked and found them to extend to 25hz, so i assume sub-bass extend well. These sounds fabulous with pop songs, but i think metalheads may not enjoy it, not because its unable to control fast song but more like because of the quantity. I listened to that Stain of time song from Metal Gear Rising and i think the beats arent sticking together, unlike my S500 which did that poorly. The bass of 200ltd has tight impact and at the same time allow bass guitar to roar, which i really adore.
+ Mid: imo the mid of 200ltd isnt overshadowred by the low, It stands out quite well, and remains clear. Male vocal is my main dish and only a very few records that has male vocal being sunk into the sea of bass, due to bad mixing/mastering. Mid isn't recess either, It feels pretty fowarded
+ High: I consider myself to have good treble tolerance, and i hardly find these to be harsh/piercing. However comapring to mid and low, it seems like the high slightly back away, giving the overall sound a darker feel, comparing to how FXT90 sounds. It is still bright sounding,i think, but just not as bright as i liked.
The thing is, Its pretty strange that some people say FXT200ltd is an upgrade from FXT90, while i find them to be rather different from each other. Whether the FXT90 is a balanced iem with slightly fowarded high, giving it a smooth and bright sound, the FXT200ltd is more of a fun sounding iem with slight emphasis on the low and lower-mid.
+Soundstage: I actually bought these for the soundstage, and boy i was not disappointed. Although it took me some time to understand the sound, i eventually realize how well these phones can do with its soundstage. While the width is just a little better than FXT90, the depth and layering is nothing but the next level on these 200ltd. To put it, with my FXT90 and S500, it sounds like I let my face being close the wall, like just 1cm close, then speak a phrase, after that I back out like a meter and say that same phrase again, that's how the 200ltd going to sound like. There's space and air to it, but not simply just having space and air, the 200ltd knows how fill that space with sound (not sure if i am overemphasizing it). Most of the time i used to listen to these iems was about rediscovering my library with the newly found and upgraded soundstage.
Another thing that i personaly found is that how unforgiving these phones can be, mostly in its soundstage department. It brings out the muddy/veiled side of many records (I mostly listen to indie/doujin stuff, home-made stuff you know) while i can overlook that with FXT90. Same for mixing, there's dfferences between amater who makes a song sound like they recorded it in a very small, tight and confined booth and a pro who makes song sound like you are in room with better positioned and layered instruments