If you gonna add a sub or plan to add one go with a 2 channel amp and let the HU power the rear.
I would not recommend you to use a 2 channel amp to power 4 speakers and bridging your speakers together. The reason why is because in most cases the rear speakers are more powerful than the fronts. If you bridge it the front speakers will start to clip while the rear speakers will still be asking for more power.
If not go with a good 4 channel one.
AVIONIXX AXA 440.4 4 CHANNEL AMPLIFIER
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=4950&item=5757802827&tc=photo
I would not recommend you to use a 2 channel amp to power 4 speakers and bridging your speakers together. The reason why is because in most cases the rear speakers are more powerful than the fronts. If you bridge it the front speakers will start to clip while the rear speakers will still be asking for more power.
If not go with a good 4 channel one.
AVIONIXX AXA 440.4 4 CHANNEL AMPLIFIER
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=4950&item=5757802827&tc=photo