Can i use the 300watts amplifier to 800w or 1000w speaker of home theatre system?

Your 300 watt reciever will work with any speaker as long as the impedance is the same. Witch most home speaker systems are 8 ohm and recievers. Some higher end equipment can do 2 or 4 ohm but you usually pay big buck's for that kind of stuff.And the other number to look for is the watt rating of the speaker of course you dont want to be putting 300 watts to 50 watt speakers.By not knowing exactly what your reciever is im guessing that when you say a 300 watt reciver that it is 150 watts x 2 if this is so any speakers with a 150 watt rating will work fine. sometimes having speakers with to high of a watt rating and to small of an amp does not do the speakers any justice and they will not sound right because they are not getting enough power to make them sound good.For example 150 watt per channel amp and 500 watt speakers the speakers wont even perform to their potential. hope this helps! Over and out..