I know there is a way to do that, but this is what I do, which is also fairly easy. For me, this works fine since I tend to want to do the same thing to all identical fixtures:
Hold the SHIFT button down while moving a specific fader. Say, let's say I want to dim all 8 of my 64 LED Pros, this will bring them all up/down at once.
Another option which is handy for color is to double click a color channel, and many fixtures will come up at once. I think now when I do this, my 64 LED Pros come up, along with my 4 Mega Panels and 4 Mega Bar 50's. I think in testing, my planned Elation opti Tri Pars come up as well. I can use a color wheel to select a color, then apply it with the penil tool to whatever fixtures I want to. Changes happen one light at a time as you make the chance, so while not all at once, it can be done as quick as you can move the mouse.
When I do the same thing for my color changers that use a color wheel, I get a choice from the color wheel colors. Same thing with my movers that use a color wheel.
But, there are way to group fixtures. In the show I do, with the 8 64 LED Pros, they are grouped 1-4 then 2-5 then 3-7 and 4-8
Light 1 is audience right, light 8 is audience right. Light 1 and 4 cover stage right, 2 and 5 cover stage right/center, 3 and 7 coover stage left/center, and lastly 4 and 8 cover stage right. I hit each area from two angles to try to do even coverage. So, if I would take a tiny bit of time, I could group these together easier. Right now I have things under control so I see no need to change.
When I redo the entire show in myDMX, I'll use the grouping more.