I wouldn't call the fx40's dark. The high end is as prominent as the low to my ears. But.
back to the main subject.
I have a large part of my small music library uploaded to google music so I can listen anywhere.
As a result, most of my listening with the xba-3 has been done on my samsung phone with the 6-8 dB boost applied to the lowest frequencies (peak at 30-32hz).
I took the the xba-3 with me to the library and since I left my phone in my car because I did not want to be disturbed, fired up google music on the library pc.
Ignoring the quality of sound coming from the pc's sound card, what immediately struck me was the sound signature difference between using it on my phone and using it on the library pc.
Most importantly. That low end wasn't gone, I just had to listen harder for it. Then I remembered I had been using it on my phone the whole time with that boost around 30hz (same with my laptop media player by the way).
So, I guess that confirms my opinion of the xba-3. I like EVERYTHING except the lowest end of the low. Not because of quality, but because of quantity. The quality always shined through when I boosted the lowest end making obvious differences and subtleties in bass notes that I hadn't previously heard.
But just to note again, this is only applicable if I decided to listen to something with sounds from that low end (like EDM or hip-hop or even songs where the bass guitar is important).
On a side note when switching back to the poor man's version of the xba-3 (mh1c), there is a clear difference. Highs, speed, soundstage, separation, bass control are on a higher level as expected. I'm even convinced that the level of bass on the mh1c is unnecessary now (though welcome). Some (Dsnuts ) have said mh1c is 80% xba-3 sound. I thought so at first but spending more and more time with the xba-3 and then comparing brings it closer to 74% with added bass.