How to switch to mains power for continued operation while charging?

Thanks in advance for your help and sorry if this has been asked before....

I'm building a portable audio system; six tweeters and two subwoofers mounted in the walls of an antique suitcase. The speakers are fed by a 48V 1200W amplifier which is in turn powered by a bank of 18650 cells putting out 48V and delivering a max 48A continuously. The cells will have their own BMS to manage charging at 1-2A. I intend to include a couple USB charging ports and a 400W 6A DC-AC inverter so that it can function as a portable battery for external devices as well. So that's a max load of 33A @ 48V if charging and otherwise simultaneously operating at peak.

My question is: How do I charge the batteries under no load while simultaneously operating the system at peak performance? I want the seamless experience of plugging in the AC adapter and having playback continue while charging begins, just as we'd expect on modern Bluetooth speakers, our phones, etc.

If you have an appropriate rectifier diode in series with the battery output to amp input, all you need is to supply the amp with a voltage just above the fully charged voltage of the battery pack.

The series diode is then reverse biassed and the battery can be treated as if its disconnected.

You could also have another diode in series with the external supply to the amp, to prevent any flow from the amp (sourced by the battery) if the supply is connected but not switched on.

Use high current schottky diodes to minimise voltage drop and power loss.