In short: yes!
In general, a higher nominal impedance (more ohms) delivers less power from the receiver/amplifier.
For example, if we look at the specifications for the receiver, the Onkyo here delivers 100W stereo RMS, which is then reduced by 33% to 66W RMS (8 ohms vs. 6 ohms).
This does not harm the receiver or the speakers; you simply have less "power".