I have an XR8600 - I am using it without Monitors. The Main/Monitor Send is sending a stonger signal to one speaker than the Main/Main send is to the other. have checked leads and speakers and know it has something to do with PA Unit. any suggestions??

On the back panel there is a section labelled Patch Bay
There are 2 small switches which assign each Power Amp to either Monitor or Main Output.
It would seem you have them both set the same at present. Set one to Monitor and one to Main, and use the corresponding Power Amp outputs direct to speakers.

Note you can send signal to external amps or powered speakers from the preamp outputs. This is really handy.
Download and print the manual from https://www.manualslib.com/manual/90516/Kustom-Kpm-8420t.html
and keep it with the mixer.

( Of course don't send speaker outputs to other amps or powered speakers )

simple !! most peavey mixers have a monitor output !! you can use that to feed new amp , and theres your volume too !!! or if your already using the monitor output , you can buy a split cable (1 in 2 outs) for main send !! this cable would have to be kept short or it will induce HUMMM !! and in real extreme cases if your using a low Z send (cant think as to why ) a device known as a (direct box) normally used by instrument sends can be used in reverse to "tap" into a low Z send and output with a unbalanced send for an amp to your other room , but hey why not just add a speaker with a volume control to it for this smaller room ? and forgo the new amp

Plug either a powered monitor or amp and then speaker into one of the aux sends. Now adjust the monitor mix using the appropriate aux send pot on each of the channel strips you want to send to the monitor. Think of the aux send pots as faders for the monitor mix the same as the main fader for the ain mix.

1. Turn the main and monitor volumes all the way down (off). Plug a cd player into channel 9/10 and play a track of music of your liking. With the main/monitor volumes still off, adjust the gain on 9/10 until the clip light turns on, then back it down until the clip light just turns off. Put the channel volume at 12 o' clock.
2. With the music still playing, turn up the mains to the desired listening level first, and then adjust the graphic eq until the music sounds good in the room. Remember or mark the position of the volume control. Do not use the channel eq on 9/10 for music that has been mastered properly, leave the eq flat. Once this step is completed then you have now set the main eq.
3. Repeat the same for monitors. Turn off the main volume and then bring up the monitor main volume to the desired level first, then set eq. Now your monitor eq is set properly. Remember or mark the position of the monitor volume.
4. Set up microphone - plug a mic into channel 1 with volume all the way down. Speak or sing into the microphone and adjust the GAIN until you see the clip light, then back down a litttle on the gain. Put the monitor and main volumes back up to the mark from step 2. Now adjust the volume and monitor send on the mic channel to the desired loudness first before adjusting the mic channel eq. Use subtractive eq method to minimize distortion and feedback. ...i.e. if the mic is bassy then turn down the lows, do not ADD highs. If the mic needs bass, turn down the highs.

I HOPE you know that the monitor send jacks are NOT powered. You MUST use either powered monitors or an external amp for these to drive speakers. Assuming you have done that, you have to turn up one or both of the monitor knobs for each channel you wish to send to the monitors at the desired level. Then you advance the monitor faders for the overall monitor level.

Yes you can - but do not use the loudspeaker outlets on the rear panel.
There are a variety of outputs on the front panel (bottom right as you look at it).
You can use the main output,  or monitor  send - (for monitor you may need to use the relevant 'send' switches on each channel to send signal to these outputs. 
You should also turn the power amp switch to main only (not main + monitor) so that the internal power amplifier is not connected to the monitor socket
You could also use the record out RCA (phono) sockets on the Peavey to connect to the CD / tape input on the main mixer.
You can download a pdf of the manual from here for more informationhttp://www.peavey-eu.com/index.php

The subwoofer MAY only have a single channel. If so, you would just use either 3 or 4 to the subwoofer.

Normally you would just tap off the main mix. The only reason I can see for using the alts is to have seperate sliders for level control.

Are you sending the main mix to the monitors or are you giving them their own mix? What about using the sub groups, use 1 for your monitor send.

Send main 1 out to your Crown. Jump Mon send to PWR am insert.

Using the mon out and the proper balanced cable follow the instrcutions found in the manual section 61.

Here is a link to the manual.
http://www.behringer.com/EN/downloads/pdf/PMP1000_P0566_M_EN.pdf