You really do need to find good experts ; hard to drive is not just a simple efficiency evaluation…The Vandy is an easy load relative to impedance and phase angle w no bizare dips. it also has pistonic drivers and a very inert cabinet. Pistonic drivers don’t include out of phase trash in the output. The waterfall and your listening at friends should tell you that. I run a set of Treo CT with either a 40 wpc tube or SS amp ( MC-240 or NAIM Atom ) Personally, i would haul the amp to friends Treo and see for yourself… if anything Nelson designs amps w grunt, headroom and drive….
Of course, room size and SPL requirements might mitigate all that….
Having said that, i’ve heard a Razz… plenty of virtues for sure…. enjoy the music and the journey