While I can't answer your question directly, all of the Decware amplifiers sound great with high efficiency speakers. The amps fall into two general categories, SET's and Push-Pull (higher power). I run the Zen Mystery Amplifier (40W) to drive Omega XRS Single Alnico High Output and Caintuck Audio Lii 15 (Single Lii Audio F15 full range drivers), both of which are slightly higher sensitivity than the X5's.
While the Decware Super Zen triode is capable of driving lots of speakers, it does best with higher efficiency speakers (95dB or greater). For me, I wanted a Decware amplifier that had built in "system flexibility", should I opt for less efficient speakers in the future. For example, the ZMA drives my much lower efficiency Vandersteen 2CE speakers easily.
So if future system flexibility is a desire, I would opt for the Decware TORII Jr or above if your budget allows. Another great attribute of the Decware amplifier and preamplifier offerings is tuning of the sound via tube rolling. While the stock tubes sound great, many folks frequently roll tubes to adjust to their listening taste. FWIW, rolling the rectifier tubes generally results in the biggest change.
Additionally, if your anywhere close to Peoria, IL consider attending Decfest 10/1 to 10/3 or arranging a listening session at Decware. It's worth the trip, here's a link to Decfest 2021 registration information:
https://www.decware.com/cgi-bin/yabb22/YaBB.pl?num=1623389104.
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