Experts: Why is preamp important?

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.

It seems like you're asking a couple questions at once. The issue of why a preamp is important is a pretty broad question, and the answer is dependent on very many variables.

The more tactical question of how do you go from your Pioneer HT receiver to the "next level" and spend your dollars most wisely also depends on a few variables, but is easier to answer. IMO, no question, buying a good amp and using the pre-outs on your Pioneer will be a substantial upgrade. You don't give a budget, either immediate or longer term, but there are any number of two-channel amps that are very affordable used, that would be a substantial upgrade, and if you can spend more, the benefit would just increase. Then, at a later date, buying a higher-end pre/pro to replace the pre/pro functions of the Pioneer would again be a substantial improvement.

Charting the path, especially in a dual-use system, requires really understanding your parameters and your priorities, but, in general, replacing the functions of a HT receiver with dedicated, higher-end separates is going to be a substantial upgrade.

Kthomas, you are right, I am asking several questions. I am generally interested in what exactly a preamp does, then I'm more specifically interested in how important it is in my upgrade path. I now have speakers in my HT system that will do justice to my critical music listening needs, so I'm trying to figure out whether I should get an integrated amp, just an amp, or possibly separates. I have some space constraints that I may have to work around as well. My amp budget is probably $2k-2.5k (maybe 3k if value is there) and I will buy used to increase value proposition. I have listened to some integrateds that I love (Mac MA6500 and the Cayin H80a), but they are quite large and neither have HT bypass. I know there are workarounds to this, but it gets more complicated. Then I started to think that maybe spending the same money on just the amplification might render bigger improvement and also simplify the process (just going pre-out to the amp and that's it). That's why I asked the preamp question.

I may also consider upgrading source, currently Pioneer dv47a universal player. I will also be upgrading my Sonos unit, probably with a Cullen mod and mayber also a standalone dac, although the dac in the Pioneer rcvr is excellent, and compares favorably to what I'm getting out of a Sonos/BelCanto DAC2 setup in my upstairs system (older B&W matrix 803s2 pwrd by Acurus DIA100 passive integrated). So I'm tackling numerous issues and trying to manage budget as well. Hopefully this gives you a little more insight into what I'm trying to accomplish.