I took almost the same path as you when I upgraded. I was using an NAD receiver with preout/powerin jacks and a phono stage. First came a new power amp, using the NAD as the preamp and phono. Then a tube preamp, using the NAD only for the phono through the tape outputs. Then finally an outboard phono stage. Only then did I clean up the NAD and sell it. It performed for 20 years, and admirably right up to the end.
You'll probably end up with all separates just as I did, but there's no reason you have to do it all at once.
You'll probably end up with all separates just as I did, but there's no reason you have to do it all at once.