This product, like the Harman Kardon power amplifier, uses the loudspeaker outputs of the Symphony as its input (according to Tom Palmer's review on the web page to which you linked). That is poor technical practice. The reviewer also says that after installation his system was no louder than it was originally, which is not too surprising.
I honestly wouldn't waste your time and money Gary. Instead, spend it on improving the loudspeakers. I think you'll find that much more rewarding.
Simon