Matt Underwood (who's 43) also does some stuff for STO during the Indians post season (MAC football/hoops, high school football playoff games), while Rick Manning (who was born in 1955 btw, so he's 56) chills, so it balances out.
Also, Underwood has a couple of young kids, so he may ask for a couple of weeks off during the season to spend with his family during summer vacation so he can play Dad.
Factor in too, that perhaps STO wants to get Al Pawlowski some booth time to call games.
And they had Hargrove do a handful of games this year to perhaps get him ready for next year (perhaps do home TV analysis with Manning in the radio booth).
Something like this:
Home games--Hamilton/Manning/Rosenhaus (radio), Underwood/Hargrove (TV)
Road games--Hamilton/Rosenhaus (radio), Underwood/Manning (TV)
The Pirates have a similar set up with former Pirate great Steve Blass doing home games, and more recent vintage ex "Bucco" John Wehner on the road.
But at the end of the day if I had to bet, I'd put credits on radio being the Hammy and Rosey show, with a new engineer being brought in.