Mine works fine with x copy and the 500a also. Yes it goes to the HD first then gets burned and my copies also come out perfect except for the warning screen and taking 2 disks.
I have DMA enabled on all the drives, I also have a 48 and 52 Liteon clone in the system and they work fine also except that any more then 2 drives burning at once is too much and one underuns eventualy.
You probably don't have the DMA enabled or some other glicth as was mentioned. Sometimes just putting drives on another IDE channel by itself will help too if you have the room.
It's nice that most new boards have IDE raid onboard plus regular IDE ports, lots of uptions and upgrade room
Some time I'll have to rearrange the drives to see if I can get 3 to burn at the same time and all work