I am running a 3.2 setup. Post calibration they were set to -1.5 for L/R and -3.5 for center, and -11.5 for each sub. I just happened to pull out the SPL meter to check things out, and noticed all levels read low (considering I've read 75dB is what they are supposed to be set to ).
This is what I am using:
Galaxy Audio CM130 Sound Pressure Level Meter https://www.amazon.com/dp/B0002GWFG4?ref=yo_pop_ma_swf
No. No app will tell you true SPL. Get a meter. https://www.amazon.com/Galaxy-Audio-CM130-Sound-Pressure/dp/B0002GWFG4