electronics don't work the way you are thinking bud... any difference between the output in the 2 amps can cause medium to large currents between the 2 amps.
to bi amp your speakers you HAVE to remove the shorting posts...
to get more power the way you are thinking, you have to get a bigger amp...
on a positive note, you did ask the question before you tried. better to ask the question, than just go charging in some times.
to get what your wanting, you should be looking at bridging channels on your amp, that will give you the result that you described above.
