I would like to add that the underseats have a ~5dB peak at around 300 - 350Hz. So, since the pink noise is full range, the meter will pick-up the level from that frequency range. To get rid of it, it is best to engage the amp's lowpass filter, at about 20-30 Hz above the the MS-8 crossover frequency. So, if you have the underseats/fronts crossed at 200Hz, set the filter to 220 - 230Hz. This way, the level will be set correctly and the MS-8 autotune can function correctly. If you don't have the option of lowpassing the signal, set the gains about 5dB louder than the other speakers.
Mobridge DA2 > JBL MS-8 > ARC XDi 600/4 > JBL Gti 408 Mids & Vifa OT19 Tweeters; PG Ti2 1600.5 > Morel HCW-10 & IDMax 15