ONLY one DMA controller for some DSP blocks??

I've developped my own set of algorithms for image processing using basic primitives in DSP Builder for an industrial project.

Now I can send a 320x240 image from memory to DSP block using two DMA controller, the first acts as image loader and the second stores the image processed by DSP block.

Each block I've designed has two Avalon FIFO-MM blocks (for RD and WR data).

I would connect all those DSP blocks to the same DMA controller and select by software from NIOS application the block I want to process the image sent.

My main question is, How can I implement this? I don't know how I must configure Avalon-FIFO MM for implementing a chip select or something like that.

Thanks in advance