When you're as good as the Marlies, there is some pretty diminishing returns on further improvement. There's only so much puck to go around, they'll bump good players out of the lineup, etc.
They can't get much better than they are.
LW Andreas Johnsson – C Miro Aaltonen – RW
Ben Smith
LW Trevor Moore – C Chris Mueller – RW Dmytro Timashov
LW
Colin Greening – C Frederik Gauthier – RW
Kyle Baun
LW Mason Marchment – C Adam Brooks – RW Jeremy Bracco
LD Andreas Borgman – RD Timothy Liljegren
LD
Martin Marincin – RD Justin Holl
LD Andrew Nielsen – RD Joe LoVerde
LD Calle Rosen
You could find a spot for them, but then you are bumping out another quality player out of the full time lineup.
Bolded are pending UFA's or RFA's who may not be qualified (Marincin). Additionally, Gauthier, Johnsson, Borgman and Aaltonen are candidates for promotion next year. I think with his injury, Aaltonen may be given the Gauthier treatment (which is fine since he's waiver exempt for another year anyways) but otherwise:
Grundstrom-Aaltonen-Korshkov (assuming they do come over)
Moore-Mueller-Timashov
Marchment-Brooks-Bracco
???-UFA-???
???/???
??? Candidates: LW/RW Vlad Bobylev, LW Nolan Vesey, RW JJ Piccinich, LW/RW Martins Dzierkals, LW/RW Nikita Korostelev, RW/C Kristian Pospisil, UFA's, LW/RW Rich Clune, LW/C Jean Dupuy (all of these guys would be on AHL contracts except maybe the UFA's).
Rosen-Liljegren
Nielsen-LoVerde
???-Holl
???-???
??? Candidates: UFA's, LD Keaton Middleton (ELC candidate), RD Nicolas Mattinen (ELC candidate), LD/RD Martin Marincin (tendered a deal; he has been a rock for the Marlies and would be great depth as much as people cringe about him but I could see him traded this offseason as well),
And absolutely nothing guaranteed in net, since both Sparks and Pickard may be dealt this offseason or claimed off of waivers, and Kaskisuo may not stick around (even though he has been solid on a 'meh' team).