Real estate sources tell TMZ ... Brantley built the house on the 12 acres of land he purchased back in 2010 ... but recently got a hankerin' for more and snapped up 300 acres of farmland nearby.

While Brantley clearly believes bigger is better ...  the 6-bedroom, 5-bath 8,446 sq ft property in Maysville, GA he's selling hardly suffers from size.

The home has all the bells and whistles of tranquil A-list living -- like a gourmet kitchen, fully equipped gym, and private safe room.

One of the best features -- a detached 68x90 man cave!

Step outside onto the 11.95 acres of picturesque land, and you'll find a heated saltwater pool surrounded by some pretty sweet professional landscaping.