Hello,
Maybe the tweeter is out in the left speaker. I agree with the cable swap or even an interconnect swap. Maybe your hearing in one ear is going out. Or try toeing in the left speaker more towards you. It could be something with your speaker crossover, but the speaker cable or maybe just swap the two speakers first. Try only one thing at a time and then put it back and try the next variable. This includes the balance control on the Luxman. Also, Do you have another pair of speakers you can try even if they are different model.