Help with an AV processor

I am wanting to use this set-up primarily for television in a bedroom. Right now I can use it with Blu-Ray and Cds but not regular television. I believe I need a processor and a sub to complete my system so I need some guidance on which pieces to get. What should I spend, what features do I need, etc? New or used works for me. Any advice is appreciated. I'm really not very knowledgeable in this area. Here is my set-up so far:

Panasonic Plasma TV
Oppo-BDP-105D
No pre or AV processor
KEF center channel
KEF LS50 L+R
Parasound Halo A-31 3 channel amp.