How do I hook up speakers to my amplifiers

The receiver line output feeds into the amplifiers for front, rear and subs. (you may need a equilizer
with additional outputs)
The sub amplifier drives the subwoofer from the bridged outputs.
the front and rear speakers should be fed from individual channels from the Receiver or another totally separate amplifier.

A power rating of 20 to 50 Watts RMS per channel is more than enough for Mids and Highs.

Here is how I'd hook up your system:
I would dedicate 1 power amp for the subwoofer by itself.
In that configuration: The receiver source L & R RCA's feeds the outboard power amp. If the receiver source is not a subwoofer only (low frequency only) output then you'll need to add an active 2 way high impedance crossover to eliminate any high frequency program from the sub woofer amplifier input. With an external 2-way crossover you can also adjust the sub gain and add +12 dB of bass boost. Hook the subwoofer up to the amp in a bridged mono configuration.
To adjust and balance the system out, keep the receiver tone controls or EQ flat, especially on the bass end and add the +12 dB bass boost from the crossover (turn it on) and by adjusting the subwoofer amplifiers gain. Balance to taste trying to get as linear (or flat) response across the band as possible with a broad range of music. After the system is balanced you can add a touch of bass or treble as needed for a particular song to suit your preference in listening.