As far as I've understood it, the RMS ratings are what the speakers are supposed to be able to handle "all day long", but I doubt they'll actually take it if you played a constant sinuswave at the rated RMS power - it definately differs between brands. A lot depends on the fact that music is very dynamic and don't stay at max for long...

Try this: play a 0dB test track of a suitable frequency (you can disconnect the speakers if you want to gp easy on your hearing) and measure the AC voltage on the speaker output. If you have a graph of exact speaker impedance vs frequency, look up the impedance for that frequency. If you don't have that (and the manufacturer doesn't have it on the web), use the nominal impedance (4 Ohm, 2 Ohm...). Calculate the power P as U^2/Z where U is RMS voltage measured, and Z is the impedance.

Adjust gain until voltage read corresponds to the rated power (or power given on birthsheet of amp. You might want to check the voltage fed to the amp, as many manufacturers give different power ratings depending on supply voltage to amp) U = sqrt(PxZ). Reconnect speakers and play music. You might well find that it is lower than you expected - we're not very sensitive to minor clipping in music, so you might well have it set a bit into clipping as it is today...

As for the filters, I'd highpass the fronts to keep them from playing the lowest bass, which they usually don't handle to well in the doors. Depending on the rear speakers I'd consider doing the same. Sub channel (5) looks to be always low pass filtered, just select the crossover frequency. If your sub is in a ported box, turn on the subs sonic filter. IF your box is tuned above 35 or so Hz, set the filter to 30Hz, if tuned lower than that, set it to 15Hz.
If it's a sealed box, just leave the sub sonic filter off.

/Michael