i gave it some more thought i looked at all the photos again, im currently looking at this photo
View attachment 4726870
id say increase the size of the beam, add another layer or two depending on what the unsupported legnth is, modify the size of the pocket that the beam sits in to accommodate another layer, frame a wall along the right hand side with 2x4's, make a beam pocket in the walls framing might aswell since your already there couldnt hurt helping pickup that while your there since i cant see what the concrete looks like or if its even sitting on the foundation. i'd then frame another wall out of 2x4's right infront of the hot water tank running all the way to the back wall. make another pocket inside that wall to pickup the beam on the other side that should allow you to pull the post however im not physically there you should measure the beams size and measure the distance of the unsupported legnth and check in the building code to verify that the beam can be unsupported at the distance between the walls/foundations beam pocket thats picking up the beam there are fairly simple tables you can read that is pretty straight forward heres a website i just found using google this would be useful for you.
http://www.the-house-plans-guide.com/beam-span-tables.html
if your able to do that, it would free up alot of space in your basement not having those posts in the way. then you can frame a nice size room at the bottom of the stairs and box around those vents on the ceiling with framing like you saw on the ceiling in my room. you can then insulate your grow room in your basement and you'll then have walls to put wiring in for outlets for various things you'll need.