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i dont think you need SEVEN dvd burner in one tower
when i duplicate a dvd, all i need is the one dvd burner, with the source dvd and original dvd.
I have never heard of "Droppix Recorder for Towers". I use CloneDVD for copying DVDs.
i think the best bet for using seven USB dvd drives are plugging the 6 into the back of your PC on the motherboard, and one plugged into the front of the PC.
As far as the DVD drives go, i think that LG is the best maker for drives. I have one and i got it 1 year ago for $69, and it burns fast, 16X, and supports every type of disc. No flaws on it!