Interesting that Taylor is now offering the Adi bracing with that 'upgrade package' to modify any model. I'd really like to hear what Adi bracing would do for a 614 with quilted maple. I owned a 614 flamed maple for a while, but it was just too thin for me. And I felt like the 616 just didn't have same shimmer.
I can testify that my 2012 BTO engelmann/quilted maple GA solved the provlem you articulated above. The CV bracing is also a factor in making the guitar's tone "fatter" with more depth, while the engelmann/quilted maple seems to have provided more overall warmth. It still retains the more desirable qualities of a maple guitar (good fundamentals, less overtones, etc.) with some added dimension.
RTaylor made its debut in 2006 IIRC, and purportedly (or so I've heard) was the impetus for what eventually became the "CV" bracing in production Taylors. Be that as it may, my style-2 in engel/quilted maple has warmth and mids that no other spruce I've ever played or heard has (quasi-cedar, if ya ask me), but with a crisp top end that is beautifully defined, as if each note were "outlined." This, along with a strong, authoritative bottom end whose bass timbre is deep yet focused absolutely defies its GC-sized body. Yeah, in case you can't tell, I fell big-time in
love with this guitar several years back, and everything else I've played since only reaffirms how special this style-2's voice is
In other words, my experience parallels that of StrummingF's BTO where the clarity and "forward" fundamentals of maple are all there, but with added bass and girth, as well as warmth in the mids. And FWIW, I recall some time ago Bob writing that quilted maple tends to be "rounder" in tone than flamed-maple's quicker, sharper attack due to quilted being flat sawn vs. flamed being quarter sawn. All to say that in sum, I'd be willing to bet it is this engelmann/CV bracing/quilted maple combo that play the lion's share in its "bigger" timbre when compared with other sitka/maple guits.
Edward