If it was me, I would only sell the device that I want to replace. if I'm happy with my amps and pre-amp, and wanted to upgrade my speakers, then that and that alone would be what I would be concentrating on.
I would slowly save enough money to purchase the new speakers, taking into consideration the amount I would make selling the other speakers.
I would not start from scratch with new amps and pre-amps when I am happy with them.
concentrate on the speakers only. (my opinion).
If, after you get the new speakers (hopefully matched to your existing gear), you feel the need to upgrade the amp, then do so at your own pace.
One item at a time. Plan for it and budget that way.
enjoy