I was using 2x1H xbows and didn't realize that the DPS was averaged between the 2. SO when I accidentally equipped a 2H xbow. I didn't get how my DPS went down.
I realize I also lose some of the abilities of each 1H xbow, but it does seem to be working better now with the 1H xbow (in Nightmare). Too bad I sold / salvaged all the other quivers I'd found.