I'm a little afraid to keep adding components, but in order to control the bass from the CI, I've been testing a resistor + highpass filter on the CI. I'm running a 50uF cap on the WBFK as well to improve the 4kHz response.
That helps cut the midrange all the way down, so the 1-4kHz region can come forward when I up the volume.
By the time I'm done, I'm going to have to increase the size of my earphones just to fit in all the electronics :x
Also, does anyone have any idea why my computer headphone jack produces very strong bass, and my sansa clip zip does not? As far as I can check, there are no enhancements/EQ going on in my laptop, but the bass response is nearly 5-10dB higher at the <250Hz range.
Most of the other players I tested so far behave more like my sansa clip rather than my laptop, though next week a friend is going to test with a USB DAC for accuracy.