Is there anything you don’t like about the shock currently on your 575? As you know the ISX6 is highly adjustable…maybe it’s downfall, as it can take some time to dial in if you don’t know what you’re doing or trying to achieve. There should still be some in depth guides on how to get the best from them over on MTBR. It’s an excellent shock for curing problems with certain suspension designs.
If it’s the one where you can adjust the dial on the piggyback by hand (4 settings), it’s for changing the bottom out resistance…great for quickly changing it for different terrain/jumps/drops.
EDIT: If I hadn’t have broken my Intense, I would have bought it off you in a shot if you decided to sell it.