Since I also have the Pioneer DVD-104 drive, let's concentrate on that one first. First of all, you're doing audio mode CD burns, not data mode correct?
Try turning on MC's logging for CD burning by changing the value of this registry key from zero (0) to one (1):
HKEY_LOCAL_MACHINE\SOFTWARE\JRiver\Media Jukebox\CD Writer\Logger
Then just start up Media Center and try to burn a CD. Then exit MC and find a file in the MC program directory called "cdwriter.log" and email that to me. This file gets overwritten every time you start MC, so grab it before you restart MC.
For the test, so that we're both doing the same thing, burn about 30 minutes worth of tracks. Have "direct decoding" enabled, have "use crossfade/dsp" enabled, have "test mode" disabled, set the writing speed at maximum. Use Ape files if you have them, otherwise, let me know what format the files are in.
Thanks!
johnt @ jriver.com