The first step in amplification where you take a very small signal from a dac, cd player, or turntable into a big enough signal, line stage, to be recognized by the amplifier is a very delicate and specialized task that is often neglected. This task is done by the preamp. It can be incorporated into an integrated amp or a dac without the proper attention or resources it deserves. As someone who posted here, if you try a proper preamp, you will have your answer. Once that first step is done, how good or how bad, there is not much even the best amplifier in the world can do. So, in theory, preamplification to line stage is more important than amplification if you believe in the proverbial garbage in, garbage out.
