angling soffit thats around hvac duct

i have to build a soffit around a fairly large duct in my basement recording studio. very similiar to blue bear sound, the first 2 photos: http://www.johnlsayers.com/Studio/Pages/Bluebear1.htm should i bother anglging the soffitt framing around the hvac duct work so that its not parallel with the opposing wall? the soffit is around 20ft long. here's a drawing, the soffitt is in yellow: http://www.farewelltoarms-pr.com/mainspace_SOFFIT.jpg

I'm going to assume (couldn't find a dimension) that you're dealing with relatively low ceilings overall - if that's true, then you'll most likely be putting absorbent (such as 2-3 inches of 703 fiberglas) on most, if not all the ceiling. No taller than AC ducts generally are, it would be much easier to skip the odd-angle carpentry and just put fiberglas over the duct, AFTER you box it in with a couple layers of well-caulked/mudded wallboard. I'd absorb both bottom and sides. I'm also hoping that duct does NOT run straight between the air handler and your room without at least a couple turns and some duct liner? Steve

the duct itself is cut into in 2 spots, which is how the basement is currently heated/cooled. maybe its not a duct i dont know. its large, rectangle shaped and a shiny silver paper like material covers it. it runs 20ft or so. i plan on changing this, well im going to get a company to come in and do all the mods to the duct work and what not. and in regards to the ceiling height. the ceiling joists are going to be exposed. :) sound travelling upstairs isnt that big of a concern for me. and no turns in the duct its pretty much straight for 20 ft and then it L's over into the boiler room area.

What about sound coming back down to you, and noise from the duct? Also, are you planning on heating/cooling your studio from that duct, or will it be sealed? Or is your only concern the acoustics of the room, because the heat will be turned off while you're recording, etc - I'm starting to lose track of what the question is... Steve