The curve shows the speaker is driven well below 8 ohms throughout most of the frequency range. Plus an 88dB sensitivity and a recommended amp power of 50 to 200 watts nominal. A 100 wpc tube amp will not supply the power to drive these speakers to their full potential, basically they won't sound very dynamic.
Although, I love the sound of the Cronus Magnum, it needs a more tube-friendly speaker.
The Pharaoh is a killer amp; a tube stage and a Class D amp section. It would should sound good with just about any speaker.