With coil inputs, the optimal power transfer occurs when the impedance of coil input is as close as possible to the cartridge impedance, which with the Steelhead would be the 25 setting for a Lyra with internal impedance of 5.5. With MM input and no coil, the rule of thumb is to use an resistance that is 20-50 times the cartridge impedance, which would be above 100, although according to taste and experimentation, you might like to go as high as 47k to get more 'air' from the cartridge. Again, you can tune to taste, even for the coils, although the volume will drop for the MC input above the closest impedance setting.
Input impedances are different for coils and straight MM amplification stages.
Input impedances are different for coils and straight MM amplification stages.