You can't connect the speaker outputs of the first receiver (where it's wattage is derived from) to the second receiver or you would blow out the inputs of the second receiver which is designed for very low voltage. If you connect the pre outs of the first receiver to the second receiver then you will get only the wattage of that second receiver.
Putting two separate amplifiers together to make a more powerful amplifier is called "bridging," but in general receiver amps aren't bridgable.
If your speakers are bi-ampable, you could use both receivers, one to drive the treble and one the drive the bass, I suppose, although I doubt it would end up as a big help.