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

Another thought on design and options for sonic purity. My integrated only has one input direct wired to the tube stage. Bypassed the selector circuit as I only need one input for my dac. This is another step that can deliver sonic benefits. Again, for today’s digital only systems not requiring multi-inputs or phono. Ralph that would be a nice option for the digital purist. One last idea. Please no more fuses. Simply have the on/off switch be a magnetically controlled circuit breaker of high quality. Another nice gain in sonic performance.

I don't understand the OP's original question. If you own an integrated, why would you need an integrated?  

Some people like a preamp even with an integrated because they want to use room correction like DIRAC

I have a luxman L-507z integrated amp. I havent seen anyone put a tube pre-amp on it yet. Altho with cornwalls it might be interesting. 

Mulviling and ghdprentice hit the nail on the head. A good preamp is so important. I don't mind a little coloration but a nice preamp adds body and texture. I've tried a couple times without a pre and the music was analytical and boring. I don't care what anyone says there is nothing like a good preamp in your system.  A former friend of mine argued until he was blue I was wrong.  I kept laughing and said you will not convince me because I know better.  

I wish I could remember who wrote a review on preamps in a system but they unequivocally stress they are very beneficial.