I'm not new to the softmod scene. I've been doing it for around a year and a half now. I have a V1.6 with a Samsung drive. I copied the contents of a game via FilezillaFTP on to my computer by dragging the disc contents to my desktop. I created an XISO and then burned it to a SonyDVD+R and DVD-R and also to an Imation DVD+RW, but I'm getting a "The Disc is Dirty or Damaged" error. It will boot up without any hiccups for about 10-20 seconds. I believe that I used Quix to do the backup, but this was about 6 months ago.
Using your Xbox, try running DVD2Xbox in ISO mode, then FTP the ISO to your comp, then burn the ISO.
DVD RW's (of any type, whether it's a - or a +) will not work when it comes to games... RW's are meant more for temporary storage of data from computer to computer.
You could also try Craxion 4. If any of that doesn't work, try a different type of media. In worst case scenario is the Rom on the XBox isn't getting the best possible reading of the disc.
If that still doesn't work, try getting a hold of another image file of the game you got and try burning that. (I had a similar error with Jade Empire... I had used an original disc, and made a backup of it... it didn't work, so I downloaded Jade Empire, dumped the contents of the backup to my Xbox harddrive and it worked perfectly).
Last but certainly not least, make sure that when you make your backups, the default.xbe is patched to work on modded xboxes.
Wrong.. Tevion +rw dvd's work fine on my samsungs.. as long as they are fully erased before burning.
There isn't going to be space for a dvdiso on a stock softmod drive.. It will probably overwrite dash files.. so don't bother.
Dump qwix and try clonexb (google.. easy to find) because the chances are something is going wrong with the xbe patching process.
If you are using 16x disks.. forget it.. 50/50 if they will work on dvd-r's.. +r a waste of time.
In the 1.6 it's a samsung605F drive.. they are not good drives... very picky about disks. I burned hundreds of ridata 8x-r's (silver with a purple wrapper) without a single faulty one... work on any drive too :)