It sounds like you have room treatment when you say you have it on all sides. But what room treatment? Blankets or something along those lines? Or actual acoustic room treatments? Your system profile does not list anything.
I was and might as well still suggest this just in case you don't have it. Bass trap absorption in the bass build up areas like corners. My system and room without bass traps was hard to listen to and higher SPLs. With bass traps, proper ones, my system sounds fantastic at higher SPLs. It is one of the benefits of bass traps I feel is quite significant. I think how a system sounds at low SPLs is a good way to gauge how good it is. But also how it sounds at higher SPLs is a good way to tell how the system sounds.
I was and might as well still suggest this just in case you don't have it. Bass trap absorption in the bass build up areas like corners. My system and room without bass traps was hard to listen to and higher SPLs. With bass traps, proper ones, my system sounds fantastic at higher SPLs. It is one of the benefits of bass traps I feel is quite significant. I think how a system sounds at low SPLs is a good way to gauge how good it is. But also how it sounds at higher SPLs is a good way to tell how the system sounds.