I tried doing that a few years ago. Went with highly regarded integrateds at the time and they sounded very good until I needed more power for bigger speakers, then I went back to separates.
What I found out with integrated amps (and this comes from the manufacturers that I have talked too at shows) and that is integrated amps are compromised compare to their separate offerings. If that is all you are looking for, then go for it. For example, the Hegel integrateds have a built in dac, but when you compare the integrated dac to their standalone dac, there is no comparison.
You have a nice sounding preamp, why not just upgrade your dac and phono pieces to match the quality of your preamp