Calibration isn't important if you're only listening to the M60s. But, when you add any other speaker (ie. a sub, a center, surrounds), it becomes important to balance them by calibrating.
I apologize if you're already aware of this, but I have no way of knowing your level of expertise, and I'd rather bug you with something you're already hip to, than omit something you're unaware of (so much for "never end a sentence with a prepostion"
). If you're listening to the M60s only, be sure that, in your receiver's speaker setup menu, the right and left mains (the M60s) are set to "Large." When you add the sub, you should probably set them to "Small," and be sure the sub setting is set to "yes," or "on."
