Which IDE channel should i put the BenQ 1640?
Primary Master
Primary Slave
Secondary Slave
It all depends on your setup. I have mine on my secondary channel as slave to my LG 4163.
Hi 
It doesn’t really matter most 1640’s are set to slave as default. Although master is often a users preference. Take a look here.
Always put the faster device as master. If you have a UDMA-2 burner and a UDMA-4 burner, set the UDMA-4 as master. If they’re both the same, it doesn’t matter.
My setup is like this
Primary Master = Sony 720A DMA 4
Primary Slave = Matshita DVD-RAM 9573S DMA 4
Secondary Master = Plextor 716A DMA 4
Secondary Slave = BenQ 1640 DMA 2
It seems OK to me. Do you have any problem with this configuration?
My setup:
Primary Master = WD Raptor WD740GD
Secondary Master = BenQ DW1640
Secondary Slave = BenQ DW1640
RAID 0 Array #1 = 2 x WD1200JB
RAID 0 Array #2 = 2 x WD1200JB
I get great burns on both BenQ drives.