Step down dc battery but have ability to charge it

I have a Sony self power by amp inside the same box of the woofer. It is from a house system. I do not have that unit, just the speaker.

I want to drill into the same box of the woofer

And add about 4 mid ranges and two tweeters and if possible have those extra speakers powered by the same amp of the woofer. Can the woofer be powered by a DC battery? If so, all I have is an E-go 56 volt DC. Battery pack. Can this pack be stepped down and be used. And finally all this is to be controlled by blutooth How do I do this Thank you Dave.