Maybe try checking the bass management for stereo listening. On the Denon that I have (which I think is fairly similar to yours), you can set it differently for stereo mode from multi channel mode. If your fronts are set to small and you turn the sub off manually, no frequencies below your crossover setting will be sent to your fronts, if I'm not mistaken. Even in pure direct mode.
I already did that and the settings for bass are on max. I have not been very clear though is that the speakers are being compared without a sub. When listening on stereo mode the sound is good but there still the missing part of the bass. After changing to the Sansui amp the woofers have a very nice vibration, giving me a better sound. Well the main thing is that as said before I have not been fully happy with my M22´s because I thought they lacked power when in the end it looks like my Denon was lacking the power to drive them.
