Having switched the 80wire to your burner & therefore the 40wire to your HDD (if I understood that right) you've terribly degraded the performance of the HDD. So you will have gained nothing & lost a lot in performance.
NECs are probably not the best readers of iffy discs but they are decent burners.
If after the cable swap the read buffers were all over the place it'll be because of what I've explained above and you definitely need to switch them back & get another 80wire cable for the burner.
Check your DMA settings on both the HDD and the NEC.