Important things you guys have to realise is that people have a video stream, they know what's going on. You don't have to say things like "oh hunter gets one up top", we know, we saw it.
Go deeper into the mechanics of the game, you guys can do this, you've been playing for so long. Before chokepoints discuss what kind of attack you expect will work better against the survivors and how close the attack was to the textbook. Point out good survivor placement, like, he was blocking a popular boomer spawn, which forced the boomer to walk in from china, really made the difference. At that DT1 tank, discuss the merits of rushing forward versus pulling back and where the threshold is to do so. More opinions, less commentary on hunters and shit going in and getting a pounce. We can all see that.
Next, you don't have to be talking about the game the entire time. I mean honestly, on some maps the survivor play and infected play are so similar that you could probably record one commentary track and paste it onto ten different scrims. In those times, you can talk about anything, your favourite porno, what you had for lunch and why that made you a fat POS, how much you hate Tratty, etc, etc. We're playing this for fun, it's not srs bsns.
Finally, you don't have to be talking the entire time. Let's face it, we know what's happening and we know when something's going good or going bad, the people watching the casts aren't going to be like "derp, what's a hunter?"
I know this is easier said than done and I know I might be too harsh.
Keeping the menace at bay through population control.