IOScope is a dual-channel analysis tool, which means that it uses two channels to capture a single IR. It is not presently equipped to capture more than one IR at a time.
If you need to acquire multiple IR's simultaneously, you might be interested in Electroacoustics Toolbox for Mac OS, which can capture an arbitrary number of measurements simultaneously (subject to your hardware limitations).
RoomScope includes a subset of the dual-channel measurement capability of IOScope. RoomScope 1.3 also adds single-channel IR acquisition for those who wish to use balloons or starter pistols to generate the impulse stimulus. The single-channel IR tool in RoomScope is capable of capturing IR's from multiple microphones simultaneously (subject to your hardware limitations).