Yes you can use this for 7.1 or 7.2 but in order to do so would need two "kits"

the setup: on your Receiver you would connect 1 tranmitter to you Left Surround and Back speaker terminals then 1 wireless reciver to those same speakers. then use the second transmitter for your Right Rear and Surround speakers and the second wireless reciver for those speakers.

Since everything is paired out of the box just plug in power and adjust delays and volume accordingly

if pairing is needed for some reason, say on your right speakers, then power off your left ones (both transmitter and reciver)

press connect button on Right channel transmitter for 2 seconds to set it to search mode then quickly go and press connect on reciver for 2 seconds to set it in search mode once they are connected you should be able to power up the ones that are off and both transmitters should be linked to only their respective recivers

I've had this thing for years now, never disconnected power to either the transmitter or receiver regardless of what channels I am/am not using. All is still well, so I'd say no, it's not harmful.

There is a volume knob on the little receiver that the rear speakers are plugged into but I just have that set to the highest. Then I just use the volume on my receiver that the home theatre is set up through and it does all the speakers (because the rear speakers are plugged into the home theatre receiver through the other wireless box).
This kit should work with your home theatre system, it still uses the same receiver that it would if the rear speakers were directly plugged in; it just basically shoots a wireless signal from the one box to the other. This is just a way to hide the speaker wire from running all along the room.

Turn on the Sender (small box) until the red light blinks. Turn on the Receiver (bigger box) and hold until they synch.

When that didn't work after multiple tries. . . .

On the back of the receiver (bigger box) there is a connect button, as well as the power button. I had to hold both down to make it synch.