An interview with Final Audio master designer Mitsuru Hosoo is on Hi-Fi+. The link is below.
I recently attended a meet which was attended by Final Audio and I was able to listen to all of their IEMs and their two reasonably priced Sonorous headphones. These are a bit unique in the industry since they use a combination of a BA and standard dynamic driver. They really presents the music well, IMO. I found their Piano Forte IEM series fantastic but since you don’t insert them into your ear canal you have no isolation and therefore can only be used in quiet locations. If you have a chance to listen to them absolutely take the time. Also their rebranded Sonorous IV and VI are really good. I purchased the IV. It’s one of only two closed headphones I own. I’m still burning it in but it sounds great. The combination of a BA and standard dynamic really presents the music well, IMO.