I am running a subpanel in my detached garage, 240v 100 amp panel. Distance is 170 ft. Direct burial, no conduit. Wondering what size/type aluminum to go with, 2/0 or 4/0, to comply with NEC code? By code I need the 4th (ground) wire because I will also be burying cable and data wire. Does this mean I should use "quadplex" or just use a 6 ga direct burial copper plus triplex? That 6 ga copper alone is running $.83/ft. Triplex $2.17/ft. Do I need 6 ga copper or can it be smaller? Not sure what application quadplex is for, maybe cheaper, no copper? Also what is the code for size of ground rods now, 5/8? I guess I need two per building 6ft or more apart?

Much Appreciated