1 driver per stepper requires extensive edits to the marlin firmware and takes out the easy multi function of the machine. I use my machine for a lot of things, sometimes multiple per day, stickers, milling, and printing I use the other sockets.
The 2.5A limit per driver is much higher than 2 nema 17’s need. This has been explained a few times, but here is the quick break down. nema steppers are usually rated at something like 2A at 4v or 8W, meaning at 12v (what we use) you only need .67A each which is still 8W.
You can use the expansion board but you would be over complicating things and spending extra money for no reason.