These is the most easy solution that I see, I am trying with two 89C2051, one of two for DMX-512 decoding and "search" and the other for PWM control only, they sould be to connected by serial port, (this´s not difficult included the DMX-512 receptor)
the DMX-512 receptor only write in SBUF and the PWM controller only read from SBUF to data (perhaps isn´t necessary IRQ serial in PWM)

Thanks