Thanks, you answered my question.
I was referring to the MM651 from your quote that I posted (updated quote in red). From pictures of the MM651 spacers that I have seen on a Goldwing install, they are a lot thicker than 1/8" so it sounds like the speakers could be seated closer with a 1/8" spacer which should help with the dash cover clearance issue.
I am happy with the stock speakers when riding without traffic, but in traffic or with loud pipes, the stock speakers just don't cut it.
Attachment 15140Attachment 15141Attachment 15142Attachment 15143Attachment 15144
The guy who did the Goldwing install used the stock speakers as a template to cut the MM651's and their spacers. This appears to have taken off a lot more meat than what was necessary. A template could probably be made which just accounts for the minimum amount of material to be removed which should help preserve the structural integrity of the speaker.