The size of wire depends on ohm rating of your speakers. Here is the chart you should reference. You also need to use "in wall" cl2 rated wire. I would recommend Monoprice in wall, hard to beat.

http://www.roger-russell.com/wire/wire.htm#wiretable

http://www.monoprice.com/Category?c_id=102&cp_id=10239

M80s VP180 4xM22ow 4xM3ic EP600 2xEP350
AnthemAVM60 Outlaw7700 EmoA500 Epson5040UB FluanceRT85