The DSP/BIOS graphical configuration tool is used to set up the HWIs, no vectors.asm should be needed. You would find the HWI number associated with the DMA interrupt for the processor and modify that HWI's properties to include the name of the interrupt function. Include a leading underscore for the function name under the General tab of the HWI properties, so "_DMA_Isr()" in your case. Also, under the Dispatcher tab select "Use Dispatcher". The keyword "interrupt" is not needed on the interrupt function when using the dispatcher.
Probably the easiest way for you to get this application working under BIOS is to start with a simple Hello BIOS application and then add your audio codec code to that framework.
-- bradley