Yes if you clip anything before the speakers the powered speakers are just going to amplifiy that clipped signal.

::the built in limiters are certainly limiting, but im dont think im hearing distortion... just fairly ugly compression.

You should be, the limiters are doing there job so you don't blow the speakers.

::if i were to drive the desk this hard into a system without limiters would it be more dangerous to the speakers?

Sure your sending clipped waveforms to the speakers, the only thing the amps are going to do is amplifiy the clipped signal.
You definetly need more amps and speakers for metal bands.

HTH
Bill W.