You don't need the song to load ANY STS sound if you assign it that way. I have 4 "go to" sounds in my STS banks that are the same for all my user styles, add that to the "My SOUND" tone, and that gives me 5 choices for any style I pick. If you don't have the STS set to change with style selection, the songbook should set up what ever sound set is called up.
My sound bank is like this:
My Sound: acoustic piano
STS1: Rhodes (add steel drums on Upper 2, strings on 3)
STS2: Whurlie (add vibes on 2, strings on 3)
STS3: Organ (add cheesier organs with 2&3) - velocity leslie trigger F/S
STS4: Sax section (uses Upper 1&2 - add 3 for brass section)

With these 5 sounds, I can get through 95% of my stuff that isn't song specific.