Sounds more like a server problem at CD Freaks.
On the dw1620 it maxes out at 8X on the read test. IGNORE the read test as it has nothing to with the write test.
Since you have the bandwidth @ 22MB/s try the F9 create disk and waste a disc. Click on the discinfo button and see what type of media and media code and speeds are available. Hopefully it will goto 16X. If it doesn't obviously you will not be able to test it to 16X.
Here's a scan of a working dw 1620 for your perusal: