MTX home speakers are generally very efficient. Their spl rating is usually 92dB or higher. SPL is sound pressure level, and is rated with a mic at 1 meter at 1 watt. The higher the spl, the louder the speaker at 1 watt. For every 3 dB drop in spl, you need double the amplifier power to obtain the same reading. So a 89 dB rated speaker needs twice the power to play at the same volume a 92 dB rated speaker needs. Klipsch are some of the highest, around 98dB.
Turning your dB up on your receiver will most likely introduce distortion. I would not use the dB as a volume control. To get the most out of your speakers, use a 12ga speaker wire, no longer than it has to be, get the towers in the corners of the room for best bass response, and ventilate your receiver to avoid overheating. Keeping the settings flat (not boosting your treble and bass or dB levels) should allow you to turn up your Marantz quite loud without distortion. You can also use a pure direct mode to avoid distortion.
What happens when you turn up your receiver? Are you not getting the loudness you desired?