Lol, 6Paths of Pain are not needed. Deva could solo. Animal Path could also give him a good fight. Gakido Path also(add a combination with Bansho tenin and it's overkill)
Deva could not Solo Gaara.
You forget Gaara also has full knowledge and will be as equally prepared as SM Naruto.
As for Gaara vs SO6P IMO I will defend him.
He is in a desert, which means Gaara + Desert vs Paths.
The sand can attack on it's own and bury many of the paths, then all he has to do is add pressure 200 meters below the earth and crush them.
-Asura path
-Human path
-Naraka path
Will all be dead with this one assault.
Now that Naraka path is gone, he will be ready to fight the other 3.
While Gaara hovers in his Sand shield, and uses 3rd eye to watch fight, he will be able to avoid Deva and Animal (sand will be occupying summonings) and take out Preta path by using frontal sand as distraction, and sand underneath to sand burial.
Deva and Animal will be difficult yet still be able to defeat them both.