You have to hear it to believe it. Listen to a quality preamp, then try to bypass it, source right to amp. Even easier these days with digital volume control on Jriver. For me, the sound is flat without a pre. With my tube pre (Eastern electric mini Max), the sound is alive, plucked strings sound juicy, the violin is sweeter, everything has greater presence and life. It's truly the heart of the system.
Why do people buy preamps if they can directly connect amp to stereo source/phone/PC/tv?
The purpose of preamp as I know it is to boost the signal to make it stronger. But I have never used preamps and my current system is already too loud (and sounds great) at moderate volume without preamp. Why do I see many people buying preamps even though they have powerful power amps?