But Kirwan is more interested in improving the Blues, something he feels Marshall would do. The coach views the 28-year-old, who plays in the halves in league, as a first five-eighth in union, where his playmaking and attacking kicking game would add spark to the Blues' backline.
Chris Noakes, who currently wears the No 10 jersey for the franchise, was a player recruited by Kirwan's predecessor Pat Lam, though he has impressed this season, especially early on.
But everything Marshall would bring - on and off the field - would be an exciting proposition, and one Kirwan believes is a serious possibility.
``I didn't talk to Benji but I spoke to his manager and we had a really great conversation about what Benji wants to do moving forward,'' Kirwan told Radio Sport.
``I think someone like Benji's got a lot to offer our game. He could be an outstanding rugby player.''
Marshall is thought to be dissatisfied with life at the Wests Tigers. He has been benched during an underwhelming campaign and, after also being stripped of the Kiwis captaincy in February, he could walk away from the sport all together.
Although his current contract doesn't expire until the end of next season, the Tigers have spent the last several months renegotiating with Marshall. In April he seemed set to sign a five-year, $4.8 million deal but never put pen to paper.
And now Kirwan is hopeful he will do so with the Blues, providing they can fend off reported interest from the Waratahs and Japan. Marshall would have to take a pay cut to move back to New Zealand but, with his off-the-field earning power, Kirwan thinks he would be willing.
``If he wants to come to rugby and aim for the [2015] World Cup and maybe the Olympic sevens, then we'd love to have him. I think that he's at a crossroads in his career and he needs some new challenges.''
A code switch would certainly provide that, though Marshall need only look at Israel Folau for the latest success story. Kirwan himself knows exactly what such a move would entail, having played 63 tests for the All Blacks and 35 matches for the Warriors, and he thinks Marshall has what it takes.
"Benji growing up in New Zealand, rugby wouldn't be foreign to him. I think it would be a fantastic challenge for him and open up a whole new world.
"Ten would be his position. The transition from rugby league to rugby would be subtle and I think he'd have to work really hard on those subtleties. But the way our game is moving with defensive patterns, he's probably a 10.''
With all the speculation, the Blues' current No 10 picked a poor time to underperform. Noakes had an opening stanza to forget against the Sharks - having a kick charged down, putting a kickoff out on the full and missing touch from a penalty - but he was not alone.
A second-half revival saw the Blues lead late in the game, before Riaan Viljoen's try 20 seconds from time left the visitors needing wins over the Cheetahs (away) and Chiefs (home) to have any chance of reaching the playoffs.
