The EQ depends on what device you are using to play the music. I have actually only used either the BT cable or Cipher cable (lightning with DSP), and always assumed that they had their amps tuned to work best with the iSine.
I'm not sure how well they do with a 3.5mm cable and no EQ and just an amp. I've not been impressed with my iPhone EQ unless only using bass reducer, treble reducer, or treble booster - but any other iPhone EQ setting that adds bass usually sounds bad (overdrives the input).
So, if the 3.5mm cable with an amp only needs a little treble boost, it shouldn't hurt the sound too much like doing bass boost.