I'm so sorry to hear about your husband's cancer. I wish I could provide some insight, but don't know if I can.
My mom was diagnosed with primary cardiac B-cell lymphoma in January--very rare and, as you may have experienced, a mystery to her doctors. A tumor nearly the size of a tennis ball filled her right atrium, affected the tricuspid valve and spilled into the right ventricle. The tumor was throwing off fluid like crazy--once they discovered the problem, the doctors drained over a liter of fluid from her pericardium and another 400 mLs a few days later. Probably much like you, we (and her doctors) were at a loss for treatment of this rare and complicated cancer. Fortunately she was referred to a wonderful oncologist and cancer facility. We had considerable success with slightly modified chemo (the tumor is now the size of your thumbnail) and are now trying to determine if radiation therapy is possible and safe. The hardest part has been trying make treatment decisions that will kill the cancer but still leave her with a healthy heart. She's 55 and we're certainly not ready to give her up. :)
I don't really know anything about sarcoma and its complications and treatment. I feel for you and your family as you face a rare cancer. It can be difficult, but keep fighting. I know there are a lot of people pulling for you. Good luck and keep us posted on your husband's progress.