The Dutch giants consigned English champions Manchester City to an early exit from Europe by finishing third in Group D of this year's Champions League.
With the final of this season's Europa League being played in the Dutch capital, De Boer knows the home crowd will demand a solid performance and a defendable lead to take back to Romania.
"We should be favourites in our own stadium but let's see how it works out," the Ajax manager told a press conference.
"It is only after the first match that you can say who the favourite is going to be. It is in these type of matches, especially the away tie in Bucharest, when you become a better player.
"I have experienced that myself in 1992, when we played UEFA Cup matches in Turin and Genoa, these are wonderful experiences."
Ajax have no fresh injury problems following a 1-1 Eredivisie draw against Roda, while Steaua are in a commanding position at the top of their own domestic league, which is now on a winter break.
Chelsea, last season's Champions League winners, could await the winners of this tie should they overcome Sparta Prague.
De Boer added: "It (the winter break) may be an advantage that we have (match) rhythm in our legs but, on the other hand, they are mentally fresh as they start again.
"It says enough that Steaua are currently 10 points ahead as frontrunners in the Romanian league. They have a nice balance and usually play a 4-3-3."
Steaua coach Laurentiu Reghecampf has been preparing his squad at a warm-weather training camp in Turkey.
He told www.onlinesport.ro: "Everything is in place after what we did physically in the training camps, which were long and tiring.
"I am glad we suffered no big injuries and we believe we are ready."