I'll leave details to any actual 3808 owners but somethings I'd be checking on my 3608 are...
Did you run both the autosetup and the autoEQ feature. If so, turn the EQ off and compare. I could never get the sound I wanted from the autoEQ feature.
Make sure it didn't accidentally switch to some EQ preset by accident. Worst sound I ever heard was when I somehow accidentally set my EQ to "Flat". Flat is obviously not the same as having the EQ turned off.
Speakers set to small with a crossover of 80 sounds good for my liking but double check the sub distance settings and the sub volume adjustment in the speaker setup. The auto-Setup often messes this one up as it has a hard time with DSP controlled subs. It had mine turned way down, if I remember correctly.
Double check that your knobs on the back of the sub are where you expect them to be. I know it's a "duh" thing to tell you but you never know whos fingers might have gotten back there.
When all is double checked, break out the SPL meter again and remember that SPL meters don't always work the best with LFE. Most are not designed to be accurate down at those frequencies although many people do use them for this.
I tweaked my sub by ear to find a more suitable sound for my tastes.
