While you could plug other applicances into the 1000 MIII, you should not run any appliance likely at the same time as the rest of your system, depending. (i.e, how much wattage and current you are requiring with additional)
As for your equip listed above, you have plenty of room, and are not running out of freed up amperage.
I think you have something like 1800 watts of range with a 15amp rated piece like the Monster. Totaling all of what you have, you should be well within that operating range, I believe. And you shouldn't be pulling more than 10 amps at any give time, likely.