Microchip PIC24's DMA doesn't work as expected
It seems like you are trying to handle two independent operations with the same index. I recommend using i for one and j for the other.  Also, I don't see where/how you are decrementing the DMA counter? 
I would recommend removing the second trigger code and use a decrement command instead.  This way you will see if the first trigger works properly.  After this works properly, you can add the second trigger code.