Speaker efficiency doesn't even come into consideration for me, only the sound. If I find a speaker that I like, getting the right amount of power is simple.
No simple and this is the reason you ask for active gain line stage when your power amp already 300 watt. I'm not gonna say your speakers are bad, but they are power suckers for a reason.
Efficient speakers for the sake of efficiency is just another audiophile religious cult. Feel free to drink your cool aid, I'll stick to sound quality.
We are all for sound quality here, great high efficient speakers can be driven by 2-10 watt amp and passive preamp. Professional BIG studio monitors are high efficient,
this is 101db. Main studio monitors must be absolutely neutral and must reproduce music in a control room just like in recording room where musicians are playing. High efficient is about dynamics in music, so it's about quality.