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

at a certain budget - say X, your best bet is to get the best integrated for X. When your budget is 2X, you will get a better sound by buying a preamp and a power amp. And then, as technology changes, tomorrow some company may come up with an integrated for 2X that sounds better than the separates. It's a never ending cycle...

A good>better pre is necessary if running source to PA IF the PA doesn't have level controls onboard.  Adding switching between source and PA allows for nearly anything one could desire inline between...
....which is how I've been able to be 'pre-less' ( No, not peerless, which is another issue for another day...) for quite awhile now.  A 6x6 matrix unit allows to 'daisy-chain' as desired with whatever makes the  boats float around here...
Generally and octave+parametric room correcting eq handles dB dosage daily.

'Upstream' of the matrix is the digital 'source' switching, with 8 in/out with 3 monitor loops to select (one 'main' with 2 additional) and a diy TT 3 in with a RIAA in/out control if 'upstream' from a 'Real pre' with a 'TT in' pair onboard (getting rarer of late...but I've not shopped integrateds or receivers lately either).

Yes, there is a lot of ic's involved.....'decent', but if I went sorta SOTA it'd co$t more than all else involved and would be kinda like pig lipstick. *L*
It's more set up for the arcane audio acts I'm up to and pleases these ears.

...and it's likely what one would want if one is diy'ng speakers....sans enclosures.

I'm 'into' a enclosure-less variant in one pursuit.....

Yes, you'll have to ask wtf that means.... ;)...

+1 for the comment by Soix on the tube preamp plus solid state power amp; when I switched from all solid state, then to all tube, and then to tube preamp with solid state monobloc power amps, I achieved a significantly higher level of sound quality.  I think I have hit near end state for the amount I have spent on my system that has both digital and analog sources.  Even my non-audiophile wife—who loves good music—commented on the realism … achieved with the tube/solid state combination.

...oh, I DO have a rather nice older pre I was gifted with...a long story there, as are most around my maelstrom....it's 'on-call' in the 6x6 for A/B, and has onboard room eq....

...as does the 'puter....which has 3 along with 'other' cheap tricks... 👍😎

Sometimes, AI can be your friend:

An integrated amplifier increases the strength of electrical signals to reproduce sound.  It combines a preamp, power amp, and other functions into a single unit. 

IOW, an integrated amplifier already includes a preamp so, no, if you have an integrated amplifier you should not need a stand-alone preamp.

Back in the day, preamps amplified very small electrical signals so they could then be adequately amplified by the power amplifier.  When digital players and DACs began outputting higher voltage signals, some people began using them to drive power amplifiers directly.  In those cases, the only other thing needed was a method to adjust the volume, so passive volume controls were introduced and, later, on-board volume controls began to show up in DACs.

However, some listeners began to notice that their systems sounded better with a preamp in the signal reproduction chain.  Why would a preamp be necessary when the DAC has enough output voltage to drive the power amp directly?  It turns out that having active preamp circuitry, even in cases where the DAC output offers plenty of voltage, improves the impedance ratio between the output from the DAC to the input into the amplifier, which reduces the effects of the interconnect cables.  As with most things in audio, there are trade-offs and the success of getting good sound without a preamp depends on the length of cables, the specific equipment used, as well as listener preferences.  Therefore, one size does not fit all.