How do i connect 2 monitors to the one monitor output jack on the peavey xr 600c mixer..cheers My product not quite the one as listed from your product database but may be similar

Connect the two Behringer B215XL to the Right/Main Speaker Outputs. Monitor(s) would connect to the Left/Mon Speaker Outputs
manual is here: https://assets.peavey.com/literature/manuals/xr684fand696f_manual.pdf

Well, I would say it isn't dropping the level of "the whole pa", it is just dropping the level of the input you have plugged the fx into. Check the settings on your fx unit, there are usually input, output and mix controls that are independant of "the pa" and affect the amplitude of the signal going into your mixer from the fx unit.

Please see my previous answer.

You would come out of the Main output on the front of the mixer into the line in on the Bose.

You may find this site useful- L1 Unofficial Performers Guide

You have two monitor outputs, each controlled by a fader. Plug the amp(s) you will be using to power the monitors into these, connect the monitor speakers to the amp(s) and you're set up and ready

You CAN drive the power amps from the main amp inout jacks BUT the rest of the inout of the 8600 would be dead then. You can connect the L and R from the FX24 to either the media RCA jacks or into the channel9/10 jacks. FOr the latter, use TRS cables. Leave the two selection buttons in the up position.

First off it's outputs to your speakers. If you had an extra set of powered or amplified speakers you could "Y" cable your speaker outputs. Your passive speakers won't work without an amp. You really need powered speakers or an amp for your extra speakers. (if you had powered/amp'd speakers you could run them off one of you "aux" out for monitors. Do not daisy chain your speakers connecting twi together, you'll change the resistance/ohms and damage your speakers. Trust me, I do this for a living.

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

Sorry, but this unit does NOT support "bridged" mode. You will have to drive seperate speakers from the two seperate outputs. You would NOT get any more power if you could do bridged mode than you could with 4 ohm speakers on each of the two output channels.

Here is a link to the manual:http://www.peavey.com/assets/literature/manuals/00513220_7.pdf I didn't look at the manual for the crossover but this is probably the way I would do it. Look at page 13 in the manual : Come out of the Main out (31 in the diagram) into the main in of your crossover. Go out of your crossover Hi and Mid out setting back into Power amp In 1 (labelled 32 in the diagram). Hook your speakers that you normally use to the output jacks on the back of the Peavey. Make sure you match the output impedances. Go out of your crossover low output into the Pyle power amp and out of the Pyle into your subs. Make sure the impedance ratings of all your speakers match the output impedances of your amps. You will only be running in Mono mode as that is the signal output of the Peavey mixer. You can run faux stereo by using the Main monitor Out as 1/2 the pair and the Main Out as the other 1/2 to both channels of the crossover but you won't be getting a true stereo pan mode.