 This randomized phase II trial is studying ixabepilone to see how well it works compared to mitoxantrone and prednisone in treating patients with metastatic prostate cancer that has not responded to paclitaxel, docetaxel, or hormone therapy. Drugs used in chemotherapy work in different ways to stop tumor cells from dividing so they stop growing or die. Some tumors become resistant to chemotherapy drugs. Ixabepilone may reduce resistance to the drugs and allow the tumor cells to be killed. It is not yet known which chemotherapy regimen is more effective in treating metastatic prostate cancer 