OP, the key (if I may) is in what I said:
Impedance: 8 ohms nominal, 6.5 ohms minimum, 14 ohms at crossover point
Sensitivity: 87 dB, 1W/1m (2.83V)
Again: with a 6.5 ohm minimum impedance, they should NOT be hard for a wide variety of amps to drive.
This is the same with Fritz's speakers, and so you can stick with tubes. Just get an amp with good transformers.
Here's a brief explanation: https://youtu.be/tvTLYqB4Zfk?si=h3wM3Xwehi4SmCrX