Tannins should not affect water quality.
Make sure the ammonia is suitable (no dyes, surfactants, perfumes, or other chemicals). There is a chart somewhere in this forum (or you may have to google it) that describes how much ammonia to add to achieve a certain amount of ppm of ammonia for a given tank size. Some say the target is 4 ppm, others 2 ppm. Get the ammonia to whichever target ppm and continue monitoring it daily. I don't think you need to add more ammonia until you see it start to drop. I could be wrong...consult the stickies regarding fishless cycling for specific details. Oh yeah, remove the shrimp. With no media from other tanks it may take several weeks before you see the ammonia drop and nitrites appear. With media from an established tank you can cut the total time down to a week or so.
Regarding the driftwood, if you have a small piece of slate, a drill and stainless steel screws, you could affix the DW to the slate (which can get buried into the substrate).
