thanks for all the great info on these new posts guys.  i wasn't aware there were so many dishes available now, or that you could run multiple SWMs.
this SWM stuff is kind of complicated at first, but it really does work every time if you power up the receivers one at a time as edizzle mentioned. 
also, some HR21s don't have the slimline dish option in the setup menu.  if this happens to you, force a firmware update by pressing 0, 2, 4, 6, 8 as soon as the blue screen comes up after powering on.