H20, you can count in hd438 in the synergy section. Not a shock since the hd439 is already in there and they are near identical in sound signature. Slightly less bass on the hd438 I think I remember, but the LF could deal with that if you wanted. Although that would just be for bass mad people. The hd438 has a frequency response peak at 120Hz, which is the same frequency which is the centre for the boost of the LF switch (assuming the box+ LF switch is at the same place), so it would be madness in my eyes to boost it more!
I sure can, I heard about the problem you're encountering on low gain, have you come to a solution, I gather this is happening with only one of your headphones?
How are you enjoying the CK4 amped compared to the headphone out? It's nice to have someone with the same rig as myself. My CK4 currently has no battery, we're trying to get a new one sent over atm after an accident occurring with the first upgrade battery.
How are you liking the changes?