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.

All gear has compromises including separates. I think making an assumption that separates always sound better is flawed today. When comparing separates to integrated amps today the sound quality differences will come down to design and execution, not the number of rectangular boxes. Huge power supplies with multiple chokes, big iron and coke can sized caps all in a separate chassis is no longer the only way to build a robust power supply for a preamp. Plenty of wonderful sounding tube preamps with low part counts and brilliantly designed circuits. Circuits with very short signal paths and low noise. Backert Labs comes to mind as one example.

So one can certainly find high quality preamp sections in an integrated amp. They can be found presently and one just needs to do due diligence when shopping. Also, there are some real sonic benefits to eliminating long ICs and connectors with a well designed Int amp. These shorter signal paths do have potential sonic benefits that offset some of the advantages that separates offer. Many integrated amps out there utilizing SOTA attenuation beyond an Alps pot 🙂.

Well thought out design including internal shielding and chassis vibration control can also help mitigate the advantages of separates. Simplicity does bring the opportunity for sonic gains.

Over the years I have heard integrated amps that are sonically superior to separates costing much more. I have also heard separates outperforming more  costly integrated amps. It comes down to the design implementation of the pieces in question, not simply the chassis count. Also, we listen to complete systems and the synergistic impact of the Int amp or separates also plays a role. It seems to me there are many considerations.

I have an MSB Discrete DAC with a Premier Power Base.  it has a built-in volume control, so a preamp is unnecessary.  However, at the urging of my local stereo dealer, he lent me an ARC LS28SE to try.  I felt that it really added so little benefit that I returned it.  However, when I moved up to an ARC REF 6, there was a marked improvement across the board. So does one "need" a preamp?  I didn't, but putting the REF 6 in the system really bettered the volume control in the DAC.  I think that it is a testament to the quality of MSB's volume control that one needs a 16K preamp to better it, but better it it does!

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