Please, help me to pick the right center and surround speaker for my home theater

I have my current set up:
- Integra rdc 7
- B & K reference 200.5 
- Martin Logan Ethos ( L+ R seapker)
- I used to have Martin Logan center cinema i ( but sound not right) sold
- Definitive mythos gem for surround ( just want to upgrade new on, please recommend)
Please, help me to pick the center and surround speaker. Thanks a lot...