whart, according to the spec they are 96db efficient. I would consider that "crazy efficient".The Everest is at the very bottom of what might be considered high efficiency and at the high end of what is considered moderate efficiency.
The woofer array is 4 ohms while the rest of the speaker is 8.
An SET is inappropriate for this speaker. The woofers are in parallel and expect that the amplifier will make twice as much power into that portion of the load or barring that, half the power into the midrange and tweeter.
For a tube amp to do this it needs a lot of negative feedback, something SETs don’t have. So if you plan to use an SET, go with the AvantGarde- you will have better luck.
Due to the efficiency, you will want at least 60 watts on this speaker in most average rooms in the US (15’ x 19’ or so) if you don’t want to clip the amp.