Wiring the amp for 240vac is a good idea.
It effectively makes the power supply in the amp larger and stiffer - which will help on creshendo and with complex passages, to whatever extent the amp circuitry can do the job. The power available from the amp will not change in any significant way.
I think you are playing things way too loud - 105 dB is way too loud for an average level. Way.
Average should be about 90 -92 at the listening position.
It effectively makes the power supply in the amp larger and stiffer - which will help on creshendo and with complex passages, to whatever extent the amp circuitry can do the job. The power available from the amp will not change in any significant way.
I think you are playing things way too loud - 105 dB is way too loud for an average level. Way.
Average should be about 90 -92 at the listening position.