Pros: Balanced sound, a mild smile-shaped FR (by ear); very musical yet detailed
Cons: Fit can be a problem at first; shallow insertion; so-so isolation; can bea bit piercing in the highs for treble sensitive people
Before I get into it, I'm going to list what I did listen to the most when I evaluate the JVC.
Sayonara Zetsubou Sensei OSTs, an anime OST that features a myriad of genres, and songs that I have listened to so many times. This helps a lot because I can recognize any changes, most of the time.
Muse, mostly from the album "Black Holes and Revolutions" and "The Resistance".
A few other bands and artists on and off like Coldplay, Keane, Florence + the Machine, Adele, Bloc Party, and a few other anime OSTs like Tengen Toppa Gurren Lagann's OST and Mahou Shoujo Madoka Magica's OST. As I have seen time and again, most of anime OST cover so broad a genre that I need to listen to them.
When I'm in front of my desk, I listen to them from my laptop using Foobar 2000 through a Fiio E10 USB DAC/amp device. When I'm out and about, I use my trusty 2-year-old Nokia N8. Music are mostly in .flac and 320 kbps .mp3 when on my laptop, and only mp3 on my phone.
While I'd like to start with the usual way people write reviews, I am not experienced enough to write that way. As such, I will try to write about what I hear separately by general frequency range, and will link to YouTube samples to some of the songs that truly highlights this IEM.
Bass is punchy and very impactful, but not boomy or flabby. Just enough amount of bass for a non-basshead to love it. I think the bass extension is quite low, but as I don't listen to many bass-heavy songs, the strongest I could think are from Muse, I can't really confirm this. It's not too overpowering, although when a particular song is mastered with gobs of bass, it will deliver gobs of bass, not more, not less. IMO they are also quite accurate, but as I said before, my lack of experience does hinder this a lot.
Vocals are to die for with these, especially for female vocals. The way the vocals are presented through the JVC is just phenominal. While very slightly recessed compared to other elements of a song or instruments, they are not veiled and remain clear and detailed, even through a very busy song. I find the treble are not forward nor recessed. There is no sibilance that I could hear, and enough sparkle to brighten a song but not being painfully so.
Vocals more or less are centre, with it sounding like it comes from the back of your skull. They sound very intimate, and drowned out a bit when there's bass going on in a song. IMO the soundstage is fairly wide; I reckon it extends to 30 cm, half a meter or so left and right, but not a lot in front and behind. Instrument separation are superb; on busy tracks, such as some of the instrumentals from the aforementioned Sayonara Zetsubou Sensei OST, I can hear the different instruments playing quite well. But what's great about it is that it doesn't sound disjointed or too separate, all seem to be in sync with each other.
Overall though, I think the FXT90 is balanced on both ends in a very small 'U' shape frequency response, with a very slight bass forwardness. Also, I think this is a quite warm sounding IEM, but no 'veil' or anything covering the treble and mids.
For more thoughts, songs I find to be so perfect with these and pictures, you can check out my blog post.