I am very confident it's not the wires.
If the pattern repeats itself at regular listening intervals, most likely it is your ears picking up on something that is not right after a certain period of time. The new ICs may just be enabling this to a greater extent than prior.
More info on what sounds "bad" the third night would be helpful to facilitate some more useful feedback perhaps.
With tube gear, the tubes themselves (old? weak? not operating up to spec?) should always be an early suspect when something is not sounding right.
If the pattern repeats itself at regular listening intervals, most likely it is your ears picking up on something that is not right after a certain period of time. The new ICs may just be enabling this to a greater extent than prior.
More info on what sounds "bad" the third night would be helpful to facilitate some more useful feedback perhaps.
With tube gear, the tubes themselves (old? weak? not operating up to spec?) should always be an early suspect when something is not sounding right.