Preamp suggestions for a monoblock setup

I am in the process of upgrading my amplification from a Yamaha RX - 497 to a monoblock setup. If anybody could suggest a good preamp to match the below system, I would be grateful! I spent quite a lot (for me) on the monoblocks so I would like to keep the preamp at or below $500 new or used. It would be ideal (but not essential) if the preamp had a headphone out.

My System:
B&W 602 S3 Loudspeakers
Audio Zone Amp D2 monoblocks
Quad CDP-2