MaxQ number is a limit on the number of cards supported per domain.
For example, if you have a M8000 (which has 32 PCI-E physical slots), and you configure that as 8 domains. Then the maximum number of cards supported will be 16 (8 domains x 2 per domain MaxQ = 16).
But, in the same example above if you have 16 domains configured, then you can have 32 (16 domains x 2 per domain MaxQ = 32) physical cards supported in the server.