Are you talking theoretical or practical? Have you actually heard the Alexx driven by an SET in the 30 watt to 45 watt range?
Believe me, the Alexx needs real power. As said in Stereophile measurements "The impedance is specified as 4 ohms nominal, with a minimum magnitude of 1.5 ohms at 2.85kHz." This kills any 30W SET - electronics can not make miracles. Read more at https://www.stereophile.com/content...-loudspeaker-measurements#CAwkhjum4o31HBpd.99