That's ok wil. Bear in mind that the demo was a few years back, and hampered by some anomalous room responses. And yet the sound was so good, it's lodged in my subconscious.
And the demo was right at my most fevered pro SETs/anti SS mindset.
So, the first recollection was of amazingly good speed. Not the enhanced leading edge that I've heard in Naim, Spectral and some Class D amps, more like natural pace unhampered by veils. The only thing I've heard in SETs that match is Thomas Mayer (but on 10dB more efficient full range driver horns).
The other main takeway was of excellent texture. Here, triodes deffo have the edge, but the combination of excellent speed and suprisingly good instrumental body, and zero noise, grain or glare, really allowed the Liszts to shine. And indeed this demo remains the most emotionally connecting horns demo I've listened to, beating by a wide margin Tron 211s and Mola Class D on Liszts, Tron 211s on Trios. Only Mayer 46 tubes on Pnoes and Azzolina Gran Sferas, and homemade 45 tubes on AG Duos comes close.
Have some other thoughts on the Amp-13R best left to PM, drop me a line.