bluegoldfish42
Now i'm not sure how well this would work, but tell what you think:
King: Broodlord
Queen: Tyrant
Rooks: Zoanthropes(i'd say fex, but he probably wouldn't fit well on a chess board)
Knights: Raveners/Gargoyles
Bishops: Warriors
Pawns: Termagaunts
the monsterous creatures might prove a problem, but if its a custom made chess board there shouldn't be too much difficulty.
I feel like it should be more like
King: Broodlord
Queen: zoanthrope (Hive tyrant would not fit)
Rooks: tyrant guard, I belive they have that tough strong feel
Knights: Gargoyles or winged warriors
Bishops: Warriors or genestealers
Pawns: homagaunts or teramgants (or spinegaunts)
and the inquistion/ impearial guard
King: inquisitor/commander
Queen: caoness
Rooks: heavy weapon team or vindicare assasin (HW team may not fit) or relic bearer
Knights: sepharim
Bishops: assasin or commisar
Pawns: sisters of battle/guardsmen/greyknights