You don't have to spend a whole lot of time calibrating the audio however. Unless you are charging for a full audio calibration session, you can do a minimum and match (or better) what the receiver does in about an hour.
In just an hour, it is amazing what you can do with a cheap RTA (something like a PAA3 $399), a good tape measure (Stanley FatMax $19), a calculator ($9), and a piece of paper to scribble on with the knowledge of the formulas you need (ohms law, 1125 ft/s, hypotenuse, etc...).
[note: a cell phone with RTA app is NOT a damn measurement tool, it is a gimmick]. The SPL apps can be useful for a down & dirty level 'balancing' however (not for sub). [A weighted pink noise please].

If you want to spend several hours doing a full calibration (and making the money for doing a full calibration), you'll need more and better equipment than that. But the end result you do for the client, will be way beyond what the adjustment in the receiver can do. As you will also be adjusting the room - moving things (speakers, seating location, objects in the room), adding things (drapes along this wall, acoustic treatments hear & there) and taking things away ("What do you mean I need to remove this mirrored wall behind me?").