250 Gold + HD here. I have the NFLRZ SD channel on 155, but when I scroll over to Sunday afternoon in the guide, the channel turns from blue to green. Selecting the channel during pops up a 371 message that says "This subcription channel is available for immedge upgrade wihout a call. Press "OK" to find out more. I don't have a phone line connected, but I suspect if the channel was free, I wouldn't have to do anything anyway.
Also, NFLRZ-HD on 9467 is red and NOT mapped down to 155.
So it looks like multisport is indeed required.