Welcome:). You can try a burst rate test with Nero CD-DVDSpeed or Kprobe 2.4.2. In Kprobe, go 'info>drive' and wait a few seconds, then scroll down to the bottom and it will report the burst rate. If your DMA is properly enabled, the 'current transfer mode' in 'device manager' should be 'Ultra DMA Mode 2' (not 'dma multi-word 2') and then your burst rate should be around 22mb/s.
There is also The big LITE-ON SOSW-852S thread , since your D56A is a rebadged Liteon 852