Bryan,
bottom line is that they both make noise, they just make different noises.
The Tunzes are extremely quiet if not run on a variable speed program. They are extremely quiet if you don't have a big hood to act like a resonance chamber.
Now, if you have them run from 30%-100%, they drone and under a hood, at least in my case, they drone loudly.
You are right, the Vortech product makes that "grindy" racket when it is on reef crest, or tidal, or pulse modes etc. That's why I bought an MP60...I run it no faster than 60% and it is relatively quiet.
My Tunzes run off the Apex controller and they have a nice interface. It isn't as fancy as the Vortech modes on the WXM module, but they control nicely off the Apex controller nonetheless. I think you would do well in moving to the Tunzes if noise is a big problem for you like it is for me and you don't want to pony up for an MP60.
They are both excellent products and the MP40 is nice if it isn't run full bore, just like my MP60. During TV time, my MP60 runs at 10% and my Tunze(one now) runs at 30-50% and I can't hear either of them.
During the day, my Tunze runs 50-70% and I can hear it droning under the hood. Conversely, I can hear the MP60 "grinding" away also. For me the ability to control them and program for having the higher output noisier times when I am asleep or away and then it goes into "quiet" mode when I am home here on the couch.
I think you would do fine adding a 6105 to your tank and dialing the MP40 way back. That would be best of both worlds.