Oh thanks Vaikl,
I simply took the output from the Tascam phone socket ( 1/4 inch audio jack ) to the Amp input socket. I can also use headphones directly from the Amp.
Problem solved, I never thought about the RCA cable being the cause of the hissing.
Strange that the M-Audio fastrak interface never had the problem though. But, who cares, my hissing has gone.