I think so too. My Earthquake is no slouch, but it's definitely not in the same class as the 600 and it still sounds quite nice paired with the 600. Though like I said, this is just from dropping it in a corner and turning it on. Getting it tuned in to how it really should sound when running with the 600 is going to take a bit more work.
I'd say definitely try it out though. Play with the phase of both subs when you first set them up to see what combination gives you the least cancellation (maximum volume) in your listening position. You can use a static test tone or the "warble" setup tones from your receiver to see what works best.
