Helmet:
/summon Item ~-4 ~ ~ {Riding:{id:"WitherSkull",direction:[0.0,0.0,0.0]},Item:{id:minecraft:diamond_helmet,Count:1,Damage:363,tag:{AttributeModifiers:[{Slot:"head",AttributeName:"generic.armor",Name:"generic.armor",Amount:5,Operation:0,UUIDLeast:1,UUIDMost:1}],Unbreakable:1,display:{Name:"Obsidian Helmet"}}},Age:-32768}
Chestplate:
/summon Item ~-4 ~ ~ {Riding:{id:"WitherSkull",direction:[0.0,0.0,0.0]},Item:{id:minecraft:diamond_chestplate,Count:1,Damage:528,tag:{AttributeModifiers:[{Slot:"torso",AttributeName:"generic.armor",Name:"generic.armor",Amount:12,Operation:0,UUIDLeast:1,UUIDMost:1}],Unbreakable:1,display:{Name:"Obsidian Chestplate"}}},Age:-32768}
Leggings:
/summon Item ~-4 ~ ~ {Riding:{id:"WitherSkull",direction:[0.0,0.0,0.0]},Item:{id:minecraft:diamond_leggings,Count:1,Damage:495,tag:{AttributeModifiers:[{Slot:"legs",AttributeName:"generic.armor",Name:"generic.armor",Amount:8,Operation:0,UUIDLeast:1,UUIDMost:1}],Unbreakable:1,display:{Name:"Obsidian Leggings"}}},Age:-32768}
Boots:
/summon Item ~-4 ~ ~ {Riding:{id:"WitherSkull",direction:[0.0,0.0,0.0]},Item:{id:minecraft:diamond_boots,Count:1,Damage:429,tag:{AttributeModifiers:[{Slot:"feet",AttributeName:"generic.armor",Name:"generic.armor",Amount:5,Operation:0,UUIDLeast:1,UUIDMost:1}],Unbreakable:1,display:{Name:"Obsidian Boots"}}},Age:-32768}