Yes, FireWire is backward compatible. All you'd need is a "bilingual" cable with the appropriate 6-pin FireWire400 connector on one side and 9-pin FireWire 800 connector on the other.
But that won't get DogCowabunga the Y-cable he's hoping for (but doesn't exist). What he's looking for is a FireWire device that can be daisy-chained.
Edited by John.B - 8/1/12 at 2:11pm