It appears more people on this thread prefer to talk than to try.
It does not take a lot of time to temporally unplug most of the switching power supplies from your house and then listen to your system for some time. Plug them all back in and listen again.
If you do not trust your ears and need a visual readout to confirm what you hear, go buy a surplus line monitor that will show you what your AC looks like.
Why do you think some people prefer battery power systems over AC. It is not because batteries are "better". It is because they are isolating their system from all the switching noise being shoved into their lines from all the little wall warts. Again, try unplugging a few and see if it sounds better.
I believe there was a report from someone who stated they replaced the PS to their router with a linear and the sound improved.
I will agree that if your AC line is filled with noise, one linear may not help. It depends on how much noise that switcher you replace is producing. The switcher that comes with the SB is a major polluter. All of you that own one, try pulling it out, even when listening to CDs, DVDs, TV, Radio, whatever and see if things sound better. If you reduce the noise, by even a little bit, it should make an improvement. Replacing as many switchers with linears will make even more improvement. They can be bought for not very much money. The PE linear than eclein uses is a prime example.
Personally, I would not want to have a computer in the same room as my system. That is why I like the SB system which allow me to isolate the computer in a separate area of the house and on a separate leg with multiple isolation devices in between.
Have fun with your AB/X and "scientific" tests. I use my system to listen to music for enjoyment. I insert a new component in the system and listen for a few days. Then I switch back and play some of the same music. If I hear an improvement in the music, that component stays. Quick A/B tests highlight differences, not necessarily improvements. Extended listening is needed for that, for me.
If any of you have any more questions about power supplies or the SB systems, please drop into my circle and ask away.