parallel receivers

I have a Marantz sr-48, 2 Tannoy MX4's and a pair of Kef Cresta and have problems with loss of power when playing all 4 speakers at once. Initially, I thought maybe the receiver was not powerful enough, but on doing more research I found out the real issue has something to do with the way the power flows through the speakers and that I need to start looking for a receiver that has parallel channels instead of serial channels. I think I am using the correct terminology. Can anyone give me any advice on receivers that have this parallel function that I can look into. Price range is under $1000.

Thanks

Michael Scott