If you are using ratchet binders, and hooking the chain single (one end to a d-ring, the other to the machine), that 6600 is reduced by half.
But you also get to reduce the "load" by 1/2, so it all kind of works out. If the sum of your chain/ binder capacity equals or is greater than the equipment weight, you are good to go.
When you run the chain from trailer, through the machine and back to the trailer in a different spot, you have essentially made a "basket" in the chain, doubling its capacity. (Basket is a rigging term- you are really just doubling the chain).
I hate gov't speak, it tends to make simple things complicated.
From the link that shimmy1 posted:
Minimum Working Load Limit for Cargo Securement Devices and Systems
The aggregate working load limit of any securement system used to secure an article or group of articles against movement must be at least one-half the weight of the article or group of articles. The aggregate working load limit is the sum of: One-half the working load limit of each tiedown that goes from an anchor point on the vehicle to an attachment point on an article of cargo; and The working load limit for each tiedown that goes from an anchor point on the vehicle, through, over or around the cargo and then attaches to another anchor point on the vehicle.
