Which sounds better, in terms of quality used at moderate power (e.g. 70wpc): a pair of 99 monoblocks, 99 stereo or 909 stereo. I know this is subjective, but pointers where to start will be appreciated. I will be driving electrostatic speakers (ESL 2905, very occasionally ESL 57). I measure quality as a combination of musical resolution, low distortion, clean higher music tones' frequencies and imaging - volume and power are not what drives my appreciation.