Thank you for your input. Do you mind commenting on the sound quality differences between the two from your perception? Ie, what is it about the FA9 that you enjoy and how does it differ from the Fa7s? Thank you for sharing!
English is not my native language and I'm not a reviewer so I'll try to experiment as I can.
As I said for a period of time I have owned both the FA7S and FA9 IEMs and had the opportunity to A/B compare them to form my own opinion.
What made me decide to keep the FA9 the most is its fantastic mid band where the FA7S can't compete, the FA9 offers that detail and texture that only a high-end BA can give, thus achieving an insane focus that makes me concentrate really about what I'm hearing and i love it for my electronic music, both are recessed in the upper mids but the FA7S is more so.
About the low end the FA7S is louder but much less controlled, at high volumes the FA7S gets easily distorted and early sounds its awful BA tone while the FA9 hits deeper and behaves more like a DD bass as far as bass is concerned. its ability to keep distortion very low while giving you more layering.
however by deactivating the bass limiter via the switches on the back, in addition to consistency you also get an excellent presence, however at the expense of the mid band which retreats a little but beats really hard.
As for the high end, it's perhaps the only aspect of the FA7S that I appreciated, right amount, very airy but never sibilant.
In contrast the FA9 reaches high octaves but becomes slightly sibilant at times but still controlled with the right source.
I think the FA9 is source dependent, I use the FA9 with the Mojo 2 and I think this really gets the most out of this IEM, I think it loses a bit to other sources I have however it does proved to be still more than a step ahead of the FA7S with all sources.
I believe the fully enclosed design of the FA9 works better than the vented design of the FA7S
The ending was that I returned the FA7S back and never wanted to hear from them again