The Tykes made a miraculous escape from relegation last year but had the youngest team in the division, with an average age of 23 years and 11 days in their starting line-up.
Struber took over as boss in November and identified the importance of adding experience, signing fellow Austrians Marcel Ritzmaier and Michael Sollbauer in the January window.
Barnsley have made just two signings so far this summer, with young right-back Kilian Ludewig re-joining on loan for the season and 26-year-old midfielder Dominik Frieser signing from LASK Linz.
The top priority is now more experienced hands to complement their youthful squad in the remainder of this window, as Struber aims to build on last season’s survival.
“We know the squad is not finished,” Struber said. “We are looking at the market, at which player can help us. We need the squad a little bigger than now. We have big goals this season and for that the squad (should be) bigger with special key players.
“The big challenge is to save (keep) the players here. We have players with interest from other clubs. This is the first big (challenge), and the other is to bring interesting players here to Barnsley. This is not so easy from the financial side.
“We need players to help the team from the first second, not the same situation where we have to develop those players and maybe in the next season they’re ready for the Championship. We need a good balance, we have many talents in the squad but on the other side we need players with professional experience, who can make the young talents better.”
Struber confirmed that there was interest in bringing Doncaster Rovers captain and central midfielder Ben Whiteman to Oakwell.
“Ben is a very interesting player,” he said. “He showed me that he can play in a good style in League One and I think he is an interesting player for us. We will see what the next few days bring with him.”
After narrowly avoiding an instant return to League One last season, Struber’s focus now is on improving Barnsley further, and he hopes that his project and the special bond between the squad will prevent players from leaving the club just yet.
“I think the project here in Barnsley to make the next step, this is interesting for many players here,” he said. “I think the relationship with the players is at a good level which is helpful.
“But I’m not stupid, I understand when players get big offers and we have for one or two players a situation where we’re fighting for that player to stay here. It’s a big fight and I think the relationship is helpful, and I hope in the end the key.”
Of most concern is interest in skipper Alex Mowatt, who only has one year remaining on his current deal, but Struber said he was hopeful of a “good solution” in contract negotiations.
Struber confirmed that, with the exception of defender Ben Williams’ long-term knee injury, he has a fully-fit squad to pick from for the first-round cup tie.