Hi Ron,
I don't know anything about your mixer but I'll throw some ideas out there. You are trying to connect 4 speakers (2 towers and 2 separate subs) with two amps? How do you have it all connected with one amp?
Assuming you want stereo (2 channel) output from your mixer, you can connect the left output to one amp, and the right output channel to the other amp. On the amp side, connect the single channel coming from the mixer into the left channel input. Connect to left input for both amps, even though one of them is a right channel. Your amps are capable of running in bridged mono mode. All amps have a different requirement for setting this up, but essentially you use the positive connection of the left channel and the negative from the right and connect those to your speaker. You'll lose a little gainconnecting only one input on the amp side, you can get a few db gain if you get a splitter on the single line to each amp and connect to both left and right inputs.
If you want to connect more speakers, you can run them in parallel. By this I mean to daisy chain the speaker outputs from the towers to the sub. Do one sub for each tower. DO NOT DO THIS UNLESS YOU KNOW THE IMPEDENCE OF YOUR SPEAKERS. Your amps are capbable of 4 ohm in mono mode. If your sub and your towers are both 8ohm, you should be able to do this. Consult your documentation.
That is all I can offer without know what your mixer is capable of doing, or what the ratings are on your speakers and subs.
Good Luck with the gig.
-James