Polk Audio FX Wireless configuration advice

I know this speaker gets a bad wrap - but managed to get one for next to nothing, I thought it worth trying to upgrade my existing 5.1 setup to 7.1.

My current 5.1 setup is RTiA9s, CSiA6, FXiA6 - connected to an Onkyo TX-NR807. The speaker levels on the receiver have all been set to about -5dB by Audessey.

When hooking up the Polk Audio FX Wireless - I've done so connecting the PRE OUTS on the AV Receivers SURR BACK to the Surround Backs on the the FX Wireless transmitter.

All is working fine, however, I find to much the speaker level of the Surround channels (-5dB on receiver) - I need to set the FX Wireless to +5dB on the receiver - does that sound correct, without the possibility of causing damage? I'm assuming it's as the speaker is Active, and not amplified by the receiver.