I think you're on the right track with the Panasonic. You can "simplify" the setup to a DAC and power amplifier. With a setup like that, you won't have unused inputs and you'll very likely have better performance but it will be two boxes and will cost you 10x what you paid for the Panasonic.

The Panasonic will do the DAC, amplification and will also serve as a crossover between your satellites and the subwoofer (the crossover in the subwoofer prevents high frequencies from coming out the subwoofer, in addition to that you need filtering to prevent low frequencies from going to the satellites)

Just set the system up and slide the Panasonic under furniture somewhere and forget that it has all those inputs, outputs and other stuff you don't need.

I would also find a way to do some some listening or experiments to validate your expectation that the new system is going to be better that the Cambridge system. You really need to know what you're doing to build your own speakers.