Hi Derrick,
Not enough information to provide you with an answer. Try being specific. You can certainly change the output level of a single Element/Operator within a single Part or of a single Part within a Performance. Can you provide any details?

Ok sure

I have my Montage connected to cubase 8.5 by midi
I have midi io mode on multi
when I select a performance or several init parts something strange happens when I adjust the parts by the sliders .
If say I have two parts : part 1 slider would work as normal but part to slider will adjust and move part 1 and 2 at the same time .
If i have say 4 parts each part slider will adjust itself and part 1 at the same time as if all the sliders are linked to part 1
hope that makes sence .

In cubase I have my midi interface connected going in and out I will admit it's a rather complex set-up because I have to use two different midi interfaces to integrate my hardware gear and still have access to Cubase chord pads it works great but for some reason the channel sliders all link back to control part 1 slider .
To further confuse thing if I change the midi channel out of cubase to say channel 2 then the part 1 slider would move part1 & 2 slider and if I change the midi out of Cubase to channel 3 then part 1 slider would also move part 1 & 3 . Confused yet ?
I think it must be some type of midi setting I have wrong but I really don't know .

It's your "complex set-up" not the Montage that is the root of your issue.

This may help you, the Channel number you set in Cubase is how Cubase is re-channelizing incoming data... MIDI events include their channel number, the channel number you set echoes the data back on a single selected channel.

When transmitting on multiple channels simultaneously, it is best to set the Track Inspector's channel number to "Any" (literally, "Any"). This will allow the data to be echoed thru Cubase and back to the Montage on the channel it arrives on, thus allowing each of the multiple channels you are sending In to be sent back Out discreetly on the channel on which it arrived... instead of merging them (which is what you're describing).