How do I increase the volume of air going into my lawn sprinkler zones to blow out water for the winter?
There are probably two things at work here, the limitations of the diameter of your hose and fittings, and the volume capacity of your compressor.

You are attempting to move air through 1/2" or larger sprinkler pipes, probably many feet, and possibly many branches; you need to deliver the air into the system faster than it exits through sprinkler heads, etc., in order to build up pressure (although I think for purging a system, volume is probably more important than pressure).

Your compressor has a rating in CFM @ PSI -- this indicates how many cubic feet per minute can be delivered at a specific pressure; one 13 Gallon unit I picked at random on Google supports 3.8CFM @ 90 PSI, which is not a lot to pressurize an open system with many feet of tubing.

If your runs are not too long, you may be able to get by using two hoses in parallel to get more volume into the sprinkler system (assuming they aren't both fed by a common small fitting somewhere; it's likely that the two fittings are intended for convenience rather than parallel operation), otherwise, your best solution is probably to rent a big compressor to do the job.