Volume level of commercial CD's.

CDs don’t play too loud. Compared to what?

Your system is too sensitive. Attenuate it.

Run them through a DAC with a gain control.

There is no problem that I see with conversion. The CD's themselves play too loud and so do the FLACS that I rip. I think the mastering is just too loud for my system but Wavegain improves the volume.

Interestingly, I have a bedside radio with a weak amp and the loud FLACS sound fine there. The problem comes with my big system (Jolida tube dac and Conrad-Johnson 250 watt amp), where the volume knob has to be at a very low setting.

Sounds like a problem with your conversion program. I recommend xrecode. Your CDs have commercials?

Wavegain sounds interesting but you can do the same thing by adding attenuators on the DAC output (or other places).