I would also like to know this. Their site lists the opamp in the Original V2, and XO, but not the Box+ or F1. I am very tempted to order But I need to know which chip this is based on. Specs show the same THD (.005%) as the AD822 that was in the V2, but 50mW higher output power.
Would also be nice if they could do a sale or special again like they did with their free shipping.
EDIT: Maybe this would get more views in the Headphone Amp forum.