I am looking for a reciever that will power my 5 speaker Polk LSi 4 ohm surround sound system. I would prefer to use a single reciever unit if possible(I know an external amp would work better but...) because space is limited. I had not plannned on replacing my current reciever (Onkyo TX-SR705) but was told it would not handle (without an external amp) the LSi's. Ideas?