You are proposing using pre-built modular buffers for the PWM signals. This sounds quite plausible; each buffer appears to be designed for a total of 12A as I read it. I note that the input voltage is specified as 2 to 5V though they suggest it is possible and intended to chain them from successive 12V strips, and that the positive is commoned; so whether you can use a different V+ for the input and output (which would suggest they are opto-isolated) is not stated.