Modifying (cheapifying) - inside out wall

One other conundrum is the distance between where I plan to have control room wall installed and vocal booth wall installed. My thinking was to avoid soffits and strange framing by having one wall on one side of existing beam and ducting and the other wall on the other side. This puts a space of about a 1'6" between walls. This large gap might actually improve isolation (or cause some weird resonance!) but it is making for some strange door arrangements. Really requires a small (1'6" ) airlock /hall section between the two doors. This is why I thought I could get two doors with large glass in place of solid doors and double window. The 1"6" space would make for a weird window set up. I really prefer a real view into the vocal booth (as opposed to video screens) - just not sure it is feasible with such a large space between walls. Not sure if there is any problem with going this route. The other choice is to build soffits around ducting and beam and somehow get a window in there and maybe just one well built door (a second door could not fit under soffit very well). The devil is certainly in the details.