I don't know much about electrostats and their need for powerful amps or not, but certainly if you EQ up the bass then that means you have to apply a negative preamp to avoid digital clipping, which is essentially lowering the volume across the whole frequency range, therefore you loose volume headroom so that increases your potential need for a more powerful amplifier - with my various headphones I don't require any additional amplification (I use Unity Gain) even though I'm using up to -12dB negative preamp, my hardest to drive headphones are only the K702 and HD600, so they're not that difficult to drive. Normally if a headphone amplifier gets your headphone to a loud enough level without signs of clipping then you don't have anything to worry about re amplifier power.Just thinking about this... a claim frequently made in the electrostat community is that very powerful third party amps are needed to drive the bass properly on many electrostatic headphones (especially the SR-007).
If this is correct, and who knows whether it is or not, would the problem be exacerbated by EQ-ing electrostatic headphones to increase the bass?