Pioneer receiver run 4 ohm speakers?

Receivers have a LOT of stuff crammed into a tight space. heat is the enemy, and 4 ohms creates a LOT of heat. You would be best off NOT using it with 4 ohm speakers.
However, if you only play at low to middle volumes and NEVER loud, you could maybe get away with it. But the first time you crank it up.. you may blow it up.

They suggest 6-16 ohm speakers.I wouldn't do it.Page 25.
[http://www.pioneerelectronics.com/pio/pe/vgn/images/portal/cit_11221/50103operating_instructions_VSX-43TX_20021231238549400.pdf]

It will work fine but cheap amps lose a lot of there power at 4 ohms.
It will also cause a lot more heat which could shorten the lifespan of your reciever. Bass might be lean at high volumes it also may all work out just fine.

If they suggest 6 to 8 ohms and do not give an output figure for 4 ohms I would probably not use them; I would check with them to be sure.