I'm no expert but I suggest that you try running your drive at PIO-4 mode rather than UDMA.
UDMA was originally setup for IDE HARD DRIVES. Many CD-Rom drives don't work well and will go into retry modes when run on UDMA.
Actually this is both a Hewlett Packard and Plextor recommendation.
I am running an ACER 52X reader as UDMA but I run the Plextor 241040A in PIO mode. I've never checked speeds but both work great. The plextor will create coasters in UDMA mode. I don't use it for reading.
Hope this helps.