If you switch to a sponge filter, don't completely switch them. Keep your current filter running and add the sponge filter. Let the sponge filter go for several months and then if you are still considering it, remove the other filter. This way the sponge filter is cycled with BB and you don't force a mini cycle that could hurt your shrimp from losing the BB in the current filter.
I'd go the route of large bucket or tarp outside, wet and dry over the course of a few weeks to force the ammonia leech to quicken up. Then put it in a bucket with an airstone and let it run for a few more weeks to ensure that you don't get any bad feelers for your shrimp. Or just go to tractor supply, buy a 50 pound bag of black diamond and sell the amazonia to someone else :P. Am I the only who thinks it's crazy that such an expensive substrate will kill your critters if you are unaware of the ammonia spikes before using it?