Sound quality impact - preamp vs power amp?

On my system, I get more sound difference from power amps than preamps. 
My power amps - Plinius SA102, Audio Research 150M.2, Jungson JA99C. 
My pre amps - Plinius M16-P, PrimaLuna Dialogue Primium, Jungson JA1.
On my most recent upgrade path, I decided to upgrade Plinius SA102. 
Anyway, your system will be always bound to the weakest link. The power amp and the preamp should be comparable.