if your preamp has low output impedance and your power amp has high input impedance (typical of SS gear) then cable length should make very little difference. The difference should be inaudible in the majority of cases. The only worry might be noise or ground loops....in which case a longer cable is more likely to be at a slight disadvantage compared to a relatively short one.
I have made 75' runs of line level succesfully in the past. Studios use long runs of line level cabling with few problems (although they tend to use XLR cables for better noise protection)
I have made 75' runs of line level succesfully in the past. Studios use long runs of line level cabling with few problems (although they tend to use XLR cables for better noise protection)