Passive Pre-amp: Improves overall sound quality??

I will answer part of your question. The main circuit of a passive preamp typically does not require a power supply. So no AC power required. In some cases, such as those using Light Dependent Resistors a power supply and AC power is required. You may also require power if your passive features remote control volume like the Placette RVC and no longer available Bent Tap (although I think you can still get the DIY remote kit). The idea and one of the main attractions of a passive is simplicity and to act just as an attenuators and possibly input switcher.

Now for the rest of your question spend the next several days reading this thread and I think all your questions will be answered:

Lightspeed Attenuator - Best preamp ever?

Yes a lot has been written about the passive/active debate.

In a nutshell, the math (on which all electronics is based) goes against you when you run a passive system. The Lightspeed is no exception. You can improve the situation slightly by using setups that operate at lower impedances, but then your source has to support that operation, which is not something universal to say the least.

OTOH active line sections with marginal design will be easily beaten by a passive setup. So if you want to boil it down, on the cheap use passive, if you want the best you will have to go active.

How could a passive preamp improve the sound of the amplifier?

Anyone.....

Thanks to all have been responded. I have now begun my reschooling in basic electronics.

BTW, Brownsfan: Sam's current wunderlich (I know, bad pun) is the Music First Passive pre-amps. He wants to (again) do away with all active pre-amp because of all the "nasties" they ad to the music. Yes, but at what price and convenience??

If set up correctly, a passive preamp can sound as good or better than the some of the best active preamps out there. In my system, I have a high quality stepped attenuator built into the input section of my amp. Keep the interconnect 6 feet or less from digital source to amp and make sure the input impedance of the amp is at least 10x higher than the output impedance of the source. All digital source these days have enough output voltage to drive most amps to clipping. If you listen to vinyl, it gets more complicated. This is by far the best "Preamp" I've had in my system in 25+ years.