Just update my progress. After several rounds of trials, my SSA eventually becomes a 3.2GHz band of SSA and SVA hybrid. Many thanks to tv84, elasia and folks.
But before the ultimate conversion, my SSA went bricked again. This time is due to missing of some critical files (ecomb_p, vncserver etc) and directories (/usr/bin/siglent/usr/*) under /usr/bin/siglent (mtd7). The kernel was loaded successfully but it stuck in the splash screen. Telnetd did not work as the "Firmware Update" menu could not be reached. Badly, these files were also missing in my mtd7 backup image ...
Since the filesystem of mtd7 is UBIFS, the only solution came to my mind is to mount the mtd7 backup image on a linux box, and extract the missing files from the stock FW and copy them back to mtd7. After tons of hassles, my SSA becomes functional again.
Interestingly, I didn't rename ecomb_p to ecomb; just did the rename-to-x and licence blocks tricks. Currently, vsftp and udc-xilinx.ko are still missing in my SSA but everything just goes fine.