so this may not be 100% relevant since this can work with any other pair of earphones and headphones, but since you guys are already talking about other headphones anyway I thought I would share what I've done over the weekend
finally I solved my bass imbalance problem by making an adjustable bass bypass attenuator... basically it softens the volume of every frequency except 100hz downwards, so you need to turn up the volume to get the same loudness, but you will also be turning the volume up on the bass, which is good as far as I am concerned
For each channel, the signal travels on 2 paths, one with just inline resistance , and the other with the inline resistance and an inductor which lets the bass through...
There is also a low output impedance to ground using a low value resistor, in series with a capacitor which will force the low frequencies to be sent to the drivers, in case anyone is wondering why there are capacitors in my circuit
I can use the potentiometer to adjust the ratio of how much signal from the simple and bass bypass paths get in each channel, so now I can compensate for the side with less bass, but overall it there is what feels like a 9db increase in the bass regions even at the minimum setting, its hard for me relate this with digital EQ's which I have been using thus far since this is physically making the bass louder... I have to be careful not to set it too high otherwise there is distortion
Plus now I can use my ER4SR's with high impedance amplifiers and there is no more background hiss