When you connect two pairs of speakers to an amplifier, the combined impedance is actually halved. So, when two pairs of 8 Ohm speakers are connected, the overall impedance becomes 4 Ohms, even though the individual impedance for each speaker is still 8 Ohms.

The CXA60 has a power output of 60W RMS per channel into 8 Ohms, increasing to 90W RMS into 4 Ohms

This quoted amplifier power rating is per channel. If you attach 2 pairs of 8 ohm speakers, the overall impedance halves to 4 ohms, so you'll be sending 90W per channel. This is of course then split between the two speakers attached to that channel, sending 45W to each speaker.

For the CXA80 the same as above will apply, but as the CXA80 outputs 80W RMS which is increased to 120W at 4 Ohms. This means you will get 60W to each speaker when 2 pairs are used with the CXA80.