All my meter levels are fine, both on the keyboard and mixer.
I run everything on the mixer flat, it is really only there for extra mics or channels for other instruments or inputs, if ever needed.
It is possible to boost the MAXX bass and/or treble enough to cause distortion or noise, but the volume parameter can safely be raised quite a bit, and in fact it is agreed by most users that it is helpful, if not necessary, to get a hot enough output level. There have been complaints that the output is not hot enough by new users that have not discovered this adjustment. Apparently former PAX models didn't have it and were hotter out of the box.
I've tried pretty hard to get a handle on what the MAXX circuitry actually does, but I'm pretty much trusting my ears, and they tell me that the sound is better the way I have it than if it is left flat. Again, I don't do much at all with the e.q. settings, in the other section of the MAXX menu. Not necessary except possibly in extreme venues.
Now, the mic input level is VERY critical, and depending on the mic you use, it may be necessary to reduce the level of the styles and/or lead voices to allow enough gain on the mic. I have a mic or two that just marginally have enough gain, and I have one condenser mic that is too HOT to be usable no matter what I do, even to the extent of running it through a mixer channel first and rolling it way back there and then sending it to the keyboard input.
With the exception of this one mic, all the others I've tried can be e.q.d and adjusted to sound good.
There are two ways to use the mic. First, TC Helicon has included automatic processing that samples the mic signal and instantly adjusts the parameters to your voice, optimizing the e.q. You can dial up or down the amount of automatic processing. The Compressor, Gate, De-esser settings also work the same way.
Or, you can do everything manually, setting e.q. levels for lows, mids and highs, with adjustable band parameters as well. You can also do the compressor, etc., either manually or automatically, independent of your choice of e.q. modes.
On this recording I used the automatic mic processing, set to 30%. I have tried levels all the way up to 100% and this sounds best to me. Any higher and you start fighting high end feedback if you are too close to the PA. There is also an independent automatic setting labeled Warmth, which when selected adds additional processing that seems to add a little more sparkle to the high end and at the same time a little more warmth to the mids. In other words the mic circuitry is very sophisticated and allows you to waste untold time playing with settings if you wish!
On the external Harmony M processor that I formerly used, I always turned the automatic processor all the way to 100% and it sounded great to me. This one has way more "stuff".