I just did the upgrade to remove the rivets and put in nuts and bolts on one of my 626Neo panels last night. It makes a significant difference. Even I can hear it clearly. I did a quick a/b this morning and Norah Jones hits me right between the eyes with the upgraded panel while she is sitting in the corner lazily on the still riveted panel. So, for anyone who hasn't done so, I suggest you change your mids from riveted to riveting
Now to find some time to do the other one.
Neil.