Yeah you need the bbs software for this BCM7424 cpu to make a I2C (Jtag) connection with the cypress board, and that, I do not have.

As for the nand flash chip replacements,
You must program the new nand flash chip before placing it on the board, otherwise it still not works because you can not flash the empty chip by the usb.
For this, you must at least have the correct Cfe file on the chip programmed to bring the usb port flash method back to life.

Thus, you must have a working copy (binaries file) from a working duo2 box and programming it to the new nand flash chip before you place it on the board.

I could help you on a bin file, made from an original duo2 box, which you can use with your nand flash programmer, if you have the socket tsop48 for it.
You need this socket to place the nand flash chip onto your programmer.