Hi Dazzdax,
I haven't personally heard the Soundlabs or the Gruensch amps, but most electrostatic speakers have an inverse relationship between impedance and frequency or at least they rise in the bass and likely drop in the treble. If the Gruensch is a SS amp, it's possible your bass and lower midrange would be leaner while the highs more pronounced. If the Gruensch is typical tube amp, disregard what I just wrote.
Good luck,
Jordan
I haven't personally heard the Soundlabs or the Gruensch amps, but most electrostatic speakers have an inverse relationship between impedance and frequency or at least they rise in the bass and likely drop in the treble. If the Gruensch is a SS amp, it's possible your bass and lower midrange would be leaner while the highs more pronounced. If the Gruensch is typical tube amp, disregard what I just wrote.
Good luck,
Jordan