Use a "material lift" in conjunction with a ladder or scissor lift first of all. Skip using the extendable poles/pipes. Get custom length pipes cut and threaded from a plumbing/fire sprinkler company and make sure to paint them!!! Use strut hardware to attach to the I-beam!

How severe is the angle of the trussing? Hanging TV's above people's heads is something that should be tripple over engineered to error on the side of saftey. Use saftey chains also if possible. Attach C-clamps as stops to prevent the TV's from sliding or have a welder tack up something to prevent the sliding if the angle is severe.