More of an issue than efficiency actually: Those are 4 ohm nominal impedance speakers, a bad match for a tube amp.
Options for best performance including ability to go loud unfettered:
1) Higher power Class a/b SS amp with high current delivery capability. That will be larger, heavier, consume more power to operate and likely cost more. You might even go class A which magnifies all of the above to achieve a particular SPL.
2) Class D amp with similar power capabilities. Stability down to 2 ohm impedance is desirable (in any case for 4 ohm nominal). Smaller, lighter and more energy efficient. These are all I have used now for the last 10 years or so.
Tube amps can be a fun alternative but only with the right speakers. 8 ohm nominal impedance or higher. Sensitivity then comes into play mainly to determine how loud you can go.
Note that tube amps and Class D amps in general tend to soft clip, which is a desirable feature in general.

