Justin,
Your Mackie mixer the 808m the M stands for Mono, so you do not have a Pan, because the Left & Right is summed together.
If it was Stereo it would be a 808S.
Because it is not a Stereo Powered Mixer you have what they call the Main and the Monitor Power Amps. However with the Power Amp routing switch you can select how these Power Amps are used, either Main/Monitor setup or a Main/Main setup. This button is located to the right of the last Channel strip's XLR - 1/4" Inputs right above the EFFECTS 1/4" Send/return. Do you see it?
With the switch in the UP position, it routes to Amp1/Main and Amp2/Main
Now in the Back of the Mixer, plug one of your JBL's into
Power Amp1/Main Speaker out, pick either 1/4" jack, their Paralleled together.
Now the part that your NOT GETTING, Plug the other JBL into one of the 1/4" jacks above the markings for, Power Amp 2 / Monitor!
You now are using both Internal Power Amps and you have 300Watts per Speaker Cabinet.
Turn on the Mixer and your good to go, Mix as you usually do.
You should notice a difference though with the extra Power/Voltage being applied to your Speakers.
The Manual is not clear if the Monitor 9 Band EQ will now effect the JBL that is now plugged in to that Power Amp output, but I would think that it should. Move the Sliders and see if it effects the JBL Speaker, if it does, then you now have a seperate
EQ for each Cabinet. Also if it does, make sure that the 75Hz Rumble Reduction is set the same for both.
That's about it.
Later,
Bud