Setting amps correctly for drivers

Model of 4 channel amp?

What type boxes PD's in?

If so, this is a relatively simple operation.

RMS limiting, a safe rule of thumb that wont restrict reasonable use of your drivers is to base the limiting threshold by using ohms law to calculate the voltage achieved at 1/3rd of the RMS at the nominal impedance of the driver, so 800/3 = 267w @ 8R = 46V

Apply this limit with a slow attack and release, 2seconds attack, 8 seconds release works well for subs

Peak settings would follow the method above, substituting the values for the peak power handling ( 3200w) and using much faster attack and release times, off the order of 1ms attack, 32ms release  

Note: RMS power handling- PD drivers with their larger coils than average drivers may be fine with higher settings. My rule is never more than 100W per inch of voice coil diameter. 5” coil is therefore potentially good for 500W power dissipation. However my direct experience of looking at data of how limiters have engaged under “full output” system use, with both RMS and Peak limiters employed as per the method about rarely shows RMS limiter engagement, but frequent peak limiter engagement showing that higher RMS threshold values may not result in greater output.

Remember the 3200W "peak" rating is derived from peak voltage of the AES test signal, and peak limiter threshold is normally set referenced to RMS voltage,  I would set the peak limiter at 1600W / 113Vrms @ 8ohms, which is the same as 3200W / 160Vp @ 8ohms.  

If you measure the output voltage of the amp with your meter i would do it without a speaker connected as many amps dont like continual sine waves.  Voltage gain will not be quite accurate but if you measure 80Vrms unloaded then it shouldn't be much less at 8ohms.