I am sure that putting hours on the new cables was the reason for most of my improvement ....What makes you sure of that?
If it was a new amp, it could have been breaking in. If it was a used amp, its electrolytic capacitors might have been reforming, or it might have otherwise been recovering from a long period of sitting on a shelf.
If your speakers hadn't been in use for a significant amount of time while you were awaiting the amp, their drivers might have needed to loosen up. Or that might have been the case simply as a result of your intermittent (weekend only) usage, that effect perhaps having been less noticeable with your previous amp.
Also, your AC line voltage and/or noise conditions may have changed. RFI conditions may have changed. And are you sure that your room temperature did not change significantly, as winter approaches (temperature being a parameter that is fundamental to the physics of transistors and other semiconductors)?
If none of those possibilities are applicable, then Elizabeth's theory seems best to me :-)
Regards,
-- Al