Finishing basement - run electrical to stud wall below steel I beam
You're not going to (attempt to) drill through that I-beam to make a run for your wiring. Right? Good, don't attempt that.

It looks like the duct hanger extends about 3/4 of the I-beam, and you'll be sorely tempted to have the bottom of the soffit right under the duct. However, a bit of an air gap significantly reduces the chances of some future person (including future-you) putting a screw through the soffit and into the duct. While you're extending it, bring it down just low enough to slide a new run of NM between the frame of the soffit and the top plate of the wall.

You lose another couple of inches of headroom right there, but with a bit of work, you can dress it up nicely so it's not quite so obnoxious. Consider tapering the end upwards when you get to the door so that someone tall doesn't do a tight turn out of the stairs and smack his head into a bit of wall that only exists at head height...