I
know you mentioned you didn't want to try equalization, but........if all else fails, maybe trying a Schitt Audio Loki equalizer might help. I have read it is transparent to the source whether it is in or out of the circuit. I think the frequencies it handles are 20hz, 400hz, 4k, and 8k. Fairly cheap at $150. IMOII purchased one of these to boost the low end when listening at low volume levels at night. Basically, using it as a loudness switch. I ended up keeping it on most the time due to the dramatic bass increase. Since, I've added a sub and now only use it at very low volumes (my preamp has a tape loop, so its easy to turn the eq on an off)