Exported WAV files with Dim Pro synth bass tracks freaking out on high-end Denon receiver

To produce a bass line in some of my projects, I am using a MIDI track generated from a guitar-to-MIDI interface as input to a bass synth plugin.  I've been using Dimension Pro "Synth Basses" plugins like Ballad Bass, Warm Finger Bass and Obscure 2.  I set all the notes in the bass MIDI track to a common velocity value (like 100 or 110) to get a consistent bass line volume throughout the song.
 
When I export a WAV file and play it through various reference systems, everything is good - the bass line volume is consistent, even if the bass line covers a couple of octaves.
 
BUT, on my best sound system - a high-end Denon receiver with highly-rated Burr-Brown DAC's, pushing a pair of Polk Audio tower speakers (in stereo mode) - the three or four lowest bass notes (E3, F3, F#3, G3) are always overpoweringly loud, while higher bass notes are of normal volume.  I've double-checked the receiver settings.  I'm using the Denon's "direct" audio mode, which means NO signal processing in the Denon, and I turned off the subwoofer just in case.
 
It makes no difference how I feed the audio to the Denon.  I've used both a PC running Windows Media Player (playing the export WAV files) connected to the Denon via HDMI, and a run-of-the-mill CD player playing a redbook CD burned on my studio system (directly from the export WAV files), connected to the Denon via a standard optical digital audio interface.  The sound is the same - the lowest 3 or 4 bass notes are individually, discretely way louder than the rest of the bass line.
 
I even swapped out the Polk Audio tower speakers and tried a different pair of speakers, but still get this huge, discrete volume boost on each of the lowest bass notes.
 
The volume anomaly is the same regardless of which of the previously-mentioned Dim Pro synth bass plugins I use.  They all exhibit the same issue through the Denon.
 
Has anyone ever experienced anything like this using synth bass plugins?  I have no idea why this is happening, but I'm wondering if there is something unique about the bass synth waveform that is causing the Denon's DAC's to overamplify the lowest notes.  The issue feels like a D-to-A conversion error, because it is so discrete, but why only on those few notes, and why has this never occurred with any of the other, wide variety of CD-based music that I play through that receiver?
 

Yea, is a room problem and/or a mixing problem. Getting it to translate on all stereo systems is hard to do if your room isn't tuned. Because you do not hear the true sound of the tracks and songs. So this leads to your stuff not translating on different sound systems. 

It probably is due to your mixing techniques also. But, without hearing the true sound, how could you ever mix it right?

Cj

Could it be that the samples themselves are louder (preceived loudness) even though the midi velocities are the same?
You may want to try bouncing the tracks to a wave file and then hitting them with a multiband compressor to make sure they are all level.
The above is just a guess, but honestly, it really sounds like you are hitting a resonant frequency of the speakers or the room and that is causing the bass to jump.

UPDATE - Those of you who pointed to a room problem are right.  I ran the Denon system's "Audyssey" room tuning function, and tested again with some other recordings.  It turns out that the room that the Denon sits in just resonates like crazy at around 41 Hz.

Thanks for the feedback.