Experts: Why is preamp important?

I don't know about your particular HT receiver, but, most of the HT processors and receivers I've heard, including those pushing $10k are very disappointing -- brittle, unnatural and unpleasant. If you are serious about good audio (not primarily home theater), you will need either a good linestage/amp or an integrated amp and then switch out the speakers when not doing the home theater thing. That is what a friend of mine does.

The pre-amp is as the name implies the first step in amplification. It takes a very low power signal for a source component and steps it up so that it can then be further amplified by the power amplifier. The reason a good pre-amp is important is that a bad one can add noise or "color" the source signal and then those unwanted additions are passed on to your ear through the amplified signal that comes out of your speakers. Today however, the output signals from numerous high quality sources are strong enough to not need pre-amplification hence the advent of the passive preamp which does a number of things such as allow you to switch sources and adjust channel balance but it performs no pre-amplification rather it just passes the source signal on to the amplifier to do its job.

I don't know much about the Pioneer receiver you have but typically receivers are a set of compromises to deliver a lot of functions in one box and at reasonable price. Some receivers have the reputation for strong amplification sections, others their tuners or decoders. The conventional wisdom is that separate components provide better performance but a number of high end integrated amps have been very favorably reviewed. So I think the test is in the listening, you have some good front speakers and hopefully an equally good center I wouldn't be surprised if you could do better than the sound from your receiver.

This is where your signal starts. If your preamp is the weakest link, it doesn't
matter how good everything down the chain is, you won't get the best sound.
In all the systems I have had, I found the preamp was most important . Just
my opinion.
Joe

My experience has been that pre-amps can make a big difference to the sound of a system, although it seems like it should have afairly easy job. Very few systems really need the additional gain provided by the preamp; in most cases, teh preamp reduces, not amplifies, the signal. This would be obvious if you ever tried to connect your source (CD player for example) directly to your power amp without the preamp in between. The sound would be terribly loud, perhaps even damaging your speakers (I really wouldn't recommend trying this, unless you use a CD that starts softly and builds gradually, like Ravel' Bolero.) For this reason, in a budget system, a passive preamp might be a good choice. My experience was that inexpensive preamps did way more harm thatn good, because they were passing the signal through a cheap gain stage that wasn't necessary. My friend has a Mod Wright passive pre, and I had it in my system for a couple days. I was surprised at how good it sounded.