Like Onhwy61 said, only use one mono amp and hook it up as you normally would negative to negative and positive to positive. Then set your preamp to "Mono" playback and you should be fine.
If you try to combine both mono amps on one speaker the way you were suggesting, you'll likely blow something up.
If you try to combine both mono amps on one speaker the way you were suggesting, you'll likely blow something up.