If a preamp is really all upside and no downside, as contended here by some, then the truly high end systems should have a couple of preamps daisy chained to get the best possible sound. Odd that you never see that, even when funding is no issue.
Any time a signal is processed / amplified it is changed, unless you assume the amplifier is absolutely perfect. Of course that is never the case.
If you have a deficiency in you system, like you need to add some tube warmth, or tone controls are required to balance the sound, then a preamp is potentially in order. But note that the effect of the preamp is to alter the sound to achieve some end.
I am not suggesting that there is no place for a preamp, but useful to be aware of what it is doing, both good and bad.
