One reason for that @decooney is that the ET’s have a relatively high modulus of impedance. If you bi-amp the LFT’s, the planar-magnetic panel itself is an almost purely-resistive 11 ohm load. Maggies on the other hand are nominally 4 ohms, dropping to 2 ohms at some frequencies. Tubes don’t like low impedances.
By the way, one of the few of his contemporaries Roger Modjeski respected and saw eye-to-eye with was Mike Sanders of Quicksilver Audio. Another was Tim de Paravicini of EAR-Yoshino. But then Roger was known to be somewhat ornery ;-) .
Both Maggies and ET’s are very low-sensitivity designs (low-to-mid 80’s), but as with all dipole planars that measurement ignores the back wave of the loudspeaker, half of their output!