I highly recommend the 2x4 method. In fact that was what I was gonna post until I read Marty beat me to it.
Also, at the bottom of the stairs I would try to have a couple of the low piano dollies so the tank doesn't have to sit on the floor.
This gives you lifting room once the tank is in the basement and you can roll it over to where the stand sits.
Of course, you'll want to take the stand downstairs first and have it in place (I know, stating the obvious, but...).
BTW, either day works for me but if it's Sunday, I'll be busy watching Daytona....but I can come out and say "Hi" real quick LOL.