The Sony DW-U10A is the OEM drive of the DRU-500A and it requires a special program to convert to the DRU-500A/X, so you can take advantage of the updated firmwares. If you don't convert, your OEM drive can only burn +R discs at 2.4X as the original specs of the DRU-500A. See the following link for how to convert:
The DRU-500A/X is notorious for not burning most cheap brands of 4X -R discs at 4X. The starngest thing is that some users can burn certain -R discs at 4X while others can't with the same brand of discs. Whether it's a problem of the hardware, firmware, or the quality of the media is still a mistery. So if money is no object, then get a DRU-510A instead since it has less reported problems.
However, if you are going to burn mainly -R discs, then a Pioneer A06/106D is probably a better choice. Just my two cents.