Why does my system sound better??

Old speakers sounded better than I remembered.

This is quite possibly true!

New speakers sounded better than I remembered.

This is probably true since you just listened to the old ones, and the new ones sounded so much better!

When cold some power amps boost the bias until they warm up thus making speakers sound sweeter. But my vote's for your imagination and its unlimited bias :^)

I'll second both timrhu and zargon's hypothesis.

I have noticed osmething like this many times myself- usually when hsopping for new gear. Swappoing components in and out of the system has often made the system sound better. It has nothing to do with keeping the system on vs. shutting it off, because I do not leave the amplifier on, and don't shut the cd or pre off when swapping components. I think it has to do with cleaning off the connectors. I have noticed it more when changing electronics than speakers. Maybe this is becasue the RCAs are more sensitive / scrape themselves clean better.

Why is this getting more skepticism than cryo-treated electrical outlets?

I have noticed this also. My opinion is that the overall grounding configuration has been altered and does not return to its previous state until all components are turned off and then back on again. Try cycling everthing off and then back on and see if the difference persists.