This is at least partly a fit issue. The diaphragm and your eardrum aren't moving as well as they could. The MG5hx needs a light seal, but dynamic drivers often need to be fit carefully to avoid vacuums or any negative air pressure in the ear canal. Thr result of a vacuum which keeps the diaphragm and the ear drum from moving freely is a muted, murky, closed-in sound. Break the vacuum and everything opens up and becomes more clear. This kind of thing was discussed a bit on changstar. It was a standard thing to mention when Anakin-Anax and I were talking about ciems. What I'm saying is: Release the vacuum, free Mars! Basically, it takes a bit of care at first until it becomes a habit to insert the ciems, then break the seal (often by tugging carefully on your ear at the helix or earlobe), making sure it doesn't re-vacuum. If the sound is closed and murky, do like Quaid and try again. This is a good skill for all ciems. All of them. But, the FS ciems in particular as they are dynamics with a light seal. However, even deepthroat multi-multi BAs will benefit from this.