I haven't even checked stereo receivers to see how many have that many zones versus a typical two or three.
If you can feed that many zones with a 50 wpc, you probably will get modest room volume, but definitely not enough to feel the emotion of the music or the excitement. Then you will try to crank the volume up to the top & likely then be in danger of blowing a speaker because it overstrained trying to deal with the worst end of the distortion range or blowing a channel of the receiver. Remember, more speakers are blown from too little power than too much potential power.
Offhand, I definitely think you are asking too much of a 50 wpc receiver. Any number of current model receivers will offer about three zones & I would be looking for 90-100 watts per channel.
Now , if it is the speaker selector which is offering the potential for trying to drive those four zones, even with the most typical speaker impedence of around 8 ohms, splitting up the relatively modest (for four zones certainly) power, isn't it going to exhibit a wirede in series effect of dragging the impedence way down too low to sustain. That is in the zone for destroying some of those speakers or perhaps the overextended receiver?
I am interested in replacing my old stereo reciever with the Onkyo TX-8255. I would also be adding a speaker-selector to my system to allow audio to my 8 other speakers located in my house (4 rooms with 2 speakers). The RMS power output is 50w. Is this enough power to have all of those speakers sound good if all of them are on at one time?