That’s an unfortunate situation for sure. I’ve had a similar issue with a specific Taylor – can’t remember the series.
We opted to alter the bracing and shave it down a bit, just in the area where the preamp was going to go. I have to say that wasn’t a lot though, I wouldn’t take it down over half of its size or anything. As long as your client is informed about potential consequences and is accepting that risk, I guess it’s an option to consider.
Seeing as it’s a 16 series, that should have the hybrid bracing pattern. Apart from having less finger braces, it’s pretty similar to the standard pattern, apart from the fact that the soundhole braces are a LOT thicker. I wouldn’t foresee any huge structural issues with altering that part; compared to the standard bracing, it is heavily overbuild anyway in that area…
You could visit http://www.martinrep.com/bracing.html for a more visual reference.
Good luck to you!