How to operate with 2 vectors Avalon-MM?

Yes, I was thinking about something like shown in the attachment. The dashed boxes are custom blocks. If you have two stream inputs on your DSP block then you can remove the 'combiner' block.

The stream FIFOs can be configured for any size. If the stream output from the SGDMA or your component in bigger than a byte (4 bytes, as an example) you can insert a stream format adapter in SOPC builder between them and the FIFO to modify the stream size. The format adapters are described in this document (http://www.altera.com/literature/hb/qts/qts_qii54021.pdf).