sending 900 watts is underpowering by 100 which isnt bad, but since u have two 4 ohm subs, you will be able to wire it to a 4 ohm load and that will be seriosly underpowering your subs, you can solve this problem if you amp is 1 ohm stable and wire you subs down to 1 ohm. your subs will still sound good with 4 ohm load.