I bought 2 4" speaker rated at 160 watts (maximal music power) at 4 ohms. Does this mean I could get 2 channel 320 watt amp (160 per channel)? Thanks

yeah, but it's usually better to overpower a speaker than to under power it.
and remember that a cheap 320 watt amp puts out less "real" power than a little more expensive 200 watt amp.
stereos are weird things..