My apologies if this was not clear.
On any non PPIMV amp I have ever had, if you put a simple signal boost in the loop it will push the volume up. No gain change and no tone change as long as it is a clean, neutral signal boost.
That same boost in front of a high gain amp or into a PPIMV amp may result in some volume increase, but mainly just more gain.
Prior to the Helix I have been using an Empress ParaEQ, which has a switchable EQ and separate switchable boost, in the loop of my Bogner Helios. I set my rhythm tone, gain and volume for sitting in the mix during most of the song. I get to my guitar solo and I want that same tone and gain at a louder volume. Hence the CLEAN boost comment and the need for it to be footswitchable. Kick in extra volume with the boost side of the ParaEQ, play solo, kick back down to rhythm volume.
I see ways to do this very same thing with the Helix in 4CM. Gain block for instance, after the amps preamp so it is feeding the preamp tone and gain level into the amps Power section at a higher level to increase volume only. Put the Gain block on a footswitch.
The Issue of it not being global comes in when I find during a given gig that the Gain blocks level I have built is too high or too low. I do now see how I can adjust it via the stomp switches edit mode and the expression pedal and it will save those settings across all Snapshots, or just manually adjust in a way that applies to all Snapshots. I will be using a few Presets though so that's a pain.
The Solo volume feature on many Mesas is great for this. My TC-100 has it and it is midi controlled. So far I've done all my Helix exploring with the TC where I am using the amps clean volume boost (Solo) controlled with midi and it is working out very well.
The TC is new and I am liking it, but I love my Helios too and want to build presets around it, which means I need the Helix to provide the boost in the loop for solos. The whole point of this thing was to ditch my pedals and big, heavy pedal board and have a lighter, more portable all in one unit.