Third-placed Salford have enjoyed their finest ever Super League campaign but lost out 18-12 at Wigan Warriors, who came second, in Friday’s qualifying tie.
Asked about playing Salford rather than Adrian Lam’s side, Powell said: “I don't think it really matters.
“You look how tight that game was, there is nothing between those two teams.
"Wigan are very tough to beat at home.
"There was a little bit between the teams last time we played Wigan, in the second half, but not an awful lot in the first half.
"Our attack was pretty blunt and we have learned a lot from that lesson we got at Wigan.
"But either way, we are going to have to beat three unbelievably good teams to win the comp’ and we are going to have a really good dig at it."
Castleford, who came fifth, lost 26-8 at Wigan in their final round game but trailed just 4-2 at half-time.
If they can overcome Salford, they will have to go to the losers of leaders St Helens v Wigan to qualify for Old Trafford.
Powell admitted: “On the night, where it all counts, we have got to be outstanding.
“We are ready to go.
"We are used to travelling over to Lancashire; it has prepared us for what we have got in front of us.
"We have the same preparation in terms of what we do when we get over there and we have got to put it all together.
"And we are three games from doing something unbelievably special, and we have to draw motivation from that."