Hi all, i can see people have fitting issues with m9, so I decided to share my experience as well. I bought m9 more than a month ago and right off the bat I had similar issues as others reported. The biggest problem with m9 is the so called suction effect. You need to understand why this happening with m9 to overcome it. M9 is totally air tight iem with zero leak, this by design m9 doesn't have any kind of vent or valve at the back (this iem is designed for performers on stage, so the seal is very important here). This, similar to other non-vented iems can create vacuum in your ear canal. This vacuum, as you can imagine, constantly apply a pull force to your ear drums. This vacuum effect won't allow your eardrums to move freely to its full potential. This will eventually makes the iem very muted (in serious cases almost like underwater effect). I had the exact same issues at the beginning. I have a sony a3 as well, since the a3 is vented design I never experienced such issue before. I did a lot of a b testing between a3 and m9, and m9 always sounded muted compared to the very lively presentation of a3. I tried both kind of ear tips which came with m9 (triple comfort and silicon). I read the other people's post about suction effect an don't inserting them too deep. In my case nothing really helped. Even if I inserted them very shallow I always felt this vacuum feeling no matter how hard I tried. Then I decided to explore other ear tips, and lo and behold the comply foam tips completely eliminated all of the issues for me. I am no scientist, but i would assume the foamy material is full of microschopic holes which will allow the pressure to normalize in your ear canal. I never had the suction effect with comply. Before you say this is a commercial for comply foam, probably chineese ripoff foam tips would do the same. I ordered some from aliexpress as well (I havent received them yet).
In a nutshell foam tips transformed m9 from a muted disappointment to a pretty damn good iem (now i like it much better than the a3). I know some people think foam tips would alter the sound. If you insert it corretly I don't think it will alter the sound at all (maybe the base becomes more punchy). I tried the a3 with foam vs silicone and didn't notice a difference.
Not everything is perfect though. Those foam tips break pretty easily, my first set lasted 2 weeks only, thats why i decided to order chineese from aliexpress.
Another note on balanced vs non balanced, for me the balanced cable changed the sound to another level again. I'm using TA-Zh1ES balanced most of the time and planning to by a balanced dap as well. Balanced made m9 even more lively and punchy... oh dat bass.
Hope this helps someone.