interesting idea. here's some ideas:
tau
-king: ethereal
-queen: Shas'o/el
-bishop: stealthsuit
-knight: battlesuit
-rook: broadside
-pawn: fire warrior

Space Marines
-king: chapter master/captain
-queen: librarian
-bishop: chaplain
-knight: jump pack marine
-rook: techmarine (with a full servo-harness, i might add).
-pawn: battle brother