We can talk about firing arcs and positioning all day, but it's really the fighters and bombers that'll decide who wins or loses a fight between a Sath and a Colossus. Both ships are supposed to have enormous fighter complements which are completely absent in the FS2 campaign. If you can negate the impact of the Sathanas' fighter wings, you don't even NEED a Colossus, you could do it with one Orion. You hit the front of the Sathanas with one bomber squadron for the BFReds, one heavy fighter squadron to knock down the flak, and a squadron or two of Perseus or Myrmidons to fly fighter cover to keep your assault force from getting paved by Maras. That leaves the other half of the Orion's fighter complement to keep the bombers off. You make sure the Strike wing jumps in on the Sathanas at least 2 minutes before the Orion shows up, and it's a pretty fair bet all four BFReds should be down. With a Colossus, it's even easier since the Colossus has a vastly larger fighter wing.
So, for us really to have any idea how it would go down, we need to know three things.
1 : How many fighters a Sath actually carries.
2 : How fast can it launch them.
3 : Can you trick them into not having their fighters already out when you show up.
The first two are kind of nebulous. We see Saths launching lots of fighters, but nothing beyond what a destroyer might carry. Obviously the game couldn't support having a hundred fighters in play at once, so this doesn't necessarily mean anything. The fighters that do get launched don't come out particularly fast, maybe one wing every 30 seconds or so. Wether this is a limitation of the ship, or of the mission, is hard to say.
The third is almost certainly a yes. The Shivans do not seem to be very tactically clever, generally allowing brute force to get the job done.
The bottom line is that a Sathanas is MUCH easier for fighters to disarm than a Colossus is, mostly because the Colossus has more cannons and they're scattered more widely across the hull of the ship. As long as you can establish fighter superiority around the front end of a Sathanas for 2 or 3 minutes, you can render it offensively helpless, and then bring in whatever destroyers you happen to have to finish it off with cannon fire.