Lower volume performance cannot be corrected by speaker wire. It's a matter of amp and speaker synergy. It's a dynamic characteristics with impedance response plot of speaker and even more to consider. In you current situation, I see that your speakers would benefit from higher power I'd say 150WPC+ to get slight improvement of lower volume listening, but best way is to look to replace them. Also I'd continue to experiment with placement and listening position which is a challenge for open baffle speakers. Adding a sub is also another wise decision for your goal.
i've never considered money spent for high-end wire wise except i guess kimber 4tc unterminated bulk when i heard the most improvement of details vs. any wire tested for any price, but after considerations above you may just as well be OK with your current wire.
i've never considered money spent for high-end wire wise except i guess kimber 4tc unterminated bulk when i heard the most improvement of details vs. any wire tested for any price, but after considerations above you may just as well be OK with your current wire.