also here is duct work on other side. we will need to be creative with some sort of soffit. we are also keeping the ceiling open...

edit... that's supposed to say 8 ft not 7 ft

Obviously you'll want to maintain as much ceiling height as possible. Your objective for the wall is to maintain the 16" center on the vertical studs and also provide places to nail the drywall along side the beam.

For the beam and duct you'll need to construct a wooden soffit. There are many articles and videols on this. I'd create this soffit enclosure before the wall partitions that surround it.

https://www.youtube.com/watch?v=2eASK8_mBu8

http://www.ifinishedmybasement.com/framing-basement/framing-around-ductwork/

You box the duct in, here is an example of typical framing around HVAC duct.

thanks for the replies. we are keeping the ceiling open so not looking to soffit in the whole ductwork. I'm trying to decide if we do just a weird soffit box up top, or bump the whole wall out a bit. we will go directly straight under the main duct, but those side ones are a bit trickier. they stick out at a weird angle. and we cant insulate the rim joist because they are in the way.

In cases like this we usually do a built-in or a closet in such areas where duct work is way off and exposed like this... This way a drop will be hidden inside a closet, etc to avoid having irregular bump-outs on the ceiling.

Something like this

Main concern when framing out a basement is try to keep everything straight and avoid irregular drops as much as possible so it looks like a regular living space and not a basement with a bunch of ducts running in all different directions with boxes built around them...

Good luck

thanks. we dont want a closet there so we are discussing a recessed bookcase. no clue how to do it, but I assume we frame kind of like a doorway/window?