Hi Bill,
At a loss for the month. But Taylor went to the 9v system in the 2007 model year. This 9v preamp not only offered markedly better battery life, but it was also revoiced. Bottom line is less mids, less "metallic" electric-guitar sounding, and simply better acoustic tone. It is a significant difference, IMHO.
In 2010, Taylor went to their 3rd-generation ES system, revising the 2-body sensor to a single-body sensor, and the preamp was also reworked. The guts went to "discrete" components, and it was revoiced again for less mids and better, more "natural" acoustic timbre. I agree wholeheartedly.
While I personally think the tonal improvement from the AA system to the first 9v system was more substantial, this latest-generation ES simply sounds more like an acoustic guitar when plugged in. Having owned all incarnations, I personally found myself having to do less "drastic" EQ-ing with each ES version. This current version really can go straight to the board/PA and sound like a good acoustic, and though I still choose to EQ a little (with a Baggs Venue), it is merely mild tonal shaping just to "sweeten" the tone up a bit.
Not only have I owned guitars with each ES generation, I've gone through
upgrading from the 3v. to the 1st-gen 9v, as well as going from the 9v to the current 3rd gen. ES. So for anyone with a pre-2010 ES who is interested in going up the the current system, I'd highly recommend it. Just IMHO, of course, but the tonal benefits of the upgrade are obvious and significant, and well worth the modest cost (buy the sytstem from Taylor and have a local authorized Taylor tech do the installation, otherwise the factory wants big bills+shipping). If you are looking at new Taylors, then this doesn't apply to you of course, but I thought I'd add that bit o' info for anyone who may be curious. Hope that helps you a bit

Edward