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I think Bronnie makes a good suggestion about thinning the weakest stems of the plant. We had a well established Phyllostachys Nigra plant that had to be moved due to building work, when it was replanted in its permanent home it sulked for a whole season, at least, and threw up some very pathetic canes. I made sure it had as close to ideal conditions as possible (as you have done) and pruned out the most spindly stems as the emerged and kept any slighty thicker ones. This summer (3 years later) it has had its best year yet and I have gone back to stripping the leaves off the lower half of the canes to reveal the black stems. I think you may have to be very patient - maybe they don't like being transplanted?!
The black one does tend towards the whippy... As already suggested, chop out some of them (I'd start with the ones that flop and annoy you the most), then chop some more when any new shoots appear next year. Feed it at the same time, mulch with manure as well, chuck any clay you might dig out from elsewhere onto it for the worms to slowly take down and water water water when its in growth. Once it begins making thick stems, it should continue to do so with minimal input from you, but it'll get there quicker if you spoil it rotten in the meantime. BTW, when you prune, cut as near to the base as you can get, otherwise you risk the cut stem wasting its energy re-sprouting from the cut all bushy and stunted.
We have a Phyllostachys Nigra which is a well established clump, planted in a slate area, after the first year it was not watered, mulched or fed. After rain it flops a little but soon stands up again. Perhaps you are cossetting it a little, maybe it needs toughening up. Good luck.