Hey Guys....haw about using a galvanized pole end....it is threaded and had a base about 3 inches across with 3 or 4 holes for screws...we used to use them why back when...
for installing another chothes rack in the closet using a galvanized pipe....you could screw the plywood onto the base with the speakers installed then just attach to the stand in a circler motion...it should work just fine....BTW....I couldn't find the z-5500 but I did find and buy the Z-5300's so I will be doing the same thing....