Speaker Efficiency

   I have been listening to my Decware 300b tube amp for a few months now. At 8 watts, I have them paired with Klipsch Forte IV at 99db efficiency, and this set up has been sounding great. This morning I connected a pair of Sonus Faber Electa Amator speakers, 6ohms at 88db of efficiency. They sound fantastic, with more weight  and depth. I understand there is a huge price difference in the two speakers, but aside from that, if I am getting 80db of volume at my chair, 8' away, what is the draw back of using lower efficiency speakers with SET amps, so long as the volume is sufficient? I did notice turn the Pre amp, the tube amp and the Roon volume towards the highest setting, it starts sounding terrible....