In my system: upgrade the preamp or amp first?

Hi, I recently purchased the B&W 802D speakers. The next step is to upgrade my preamp and amp. I currently have the Parasound Halo P3 preamp and A21 amp. I am going to have to upgrade on thing at a time. That being the case, would you upgrade the preamp or amp first? My feeling is replace the P3 preamp. The A21 amp is actually not too bad. Do you agree?