I use Elixir PB Nano HD Lights. I'm a fingerpicker and find the slightly heavier gauge on the first 3 strings a benefit, since I mostly carry the melody on those strings. They work for me, in what and how I play.
I don't own a Grand Auditorium, but if I did I would use Elixir PB HD Lights. They may be shipping with those again, but if not, HDs would be in the on-deck circle as next up.
I use this gauge on most of my 6 stringers, including both my Grand Concerts, both -J-200 Jumboes, and my Grand Orchestra. My Walnut Jumbo likes Mediums best and my Alvarez demands Light gauge. Considering it is a similar size to a Grand Auditorium and a similar shape to a Grand Orchestra, there might be some competition for the best string gauge for me and a Grand Auditorium. Especially for an x-braced spruce over rosewood model.
I fingerpick all my instruments using my nails as picks. I like having a well balanced sound and the HD gauge helps me with that. Also one of the best features of Jumbo guitars is that they produce naturally well-balanced sound, and the Taylor lineup has a lot of shapes that are jumboes or are closed related to that shape, even the smaller ones. I view the Grand Orchestra as not only a replacement for a Jumbo, but an improvement over the Jumbo.
So as Susie points out that the Medium trebles in the HD gauge help improve the sound, I also feel that using the Light gauge bass in large body guitars keeps the bass more in sync with the trebles, especially with the Rosewood 818 Grand Orchestra.
Here is a link to an Elixir and Andy Powers interview/conversation about the HD Light gauge, .013 - .053 :
https://www.youtube.com/watch?v=UbTSHDm-jIg&feature=youtu.beDon