Still I can't really get used to it's sound atm, much more open but still somehow grainy, even with the "2 Radian phragm so it must be something else that causes this.
I decided to give my BSS FDS-360 another major overhaul, it already had it's input opamps replaced from NE5532's with LM4562NA's but now I took the plunge and will replace all of the remaining (LF353) opamps with OPA2134PA.

Hell, this will be the most expensive FDS360 ever
I have all the schematics and see if I can replace some electrolytics with fancy stuff like Nichocon Muse. They are all small values so it won't cost a fortune.