Dumb question......why do you need a preamp?

You only need a preamp if you wish to add "color" to your sound. Otherwise, if you do not have these: a volume control and/or selectable input device will be enough.

@patl In my experience I’ve had less coloration (and more impact) when an active line stage is used. Passive controls are very susceptible to interconnect cable colorations; a good line state can eliminate that. The best place for a passive control, so as to prevent this problem, is inside the amplifier.

I am not an engineer and speak from personal experience as well as from consulting several audio engineer friends.
You need a preamp in most cases, primarily because it provides extra drive from the source to the power amps. Even if you have enough gain, the preamp does impedance matching so it creates synergy between the source and the power amps.   The volume control is also critical and in most cases, using a DAC with digital volume creates loss because of losing bits at lower volumes. The preamp is also useful for switching between sources if you have multiple. I had my share of experiments with different passive preamps and was always disappointed, because of hearing different anomalies (lack of dynamics, body, extreme brightness or unbalanced sound etc) so always returned to the active preamp, which, despite its flaws, better than going passive.

Zoltan

I've used high end DACs with built in volume controls and always found better performance using a dedicated preamp.

 I agree  with others here.... the question is not specific.

I've been dabbling with stereo equipment for almost 50 years and the majority of the time I've had separates. The versatility of a preamp is key for me ....like when I had my McIntosh C26 ...the stereo reverse or R&L to left or what ever gives me Jimmy Pages' guitar reversed on or off to only on or both speakers. Now I have a C46 that gives me a fine tuning feature with a built in equalizer and balanced connections for clarity. Another reason is that you can try different power amps for more versatility. Couldn't live without the preamp in my world.

an integrated is a preamp + a power amp