Maybe I missed something but you can control the volume via MIDI CC already (CC #7 actually).
And using the Remote you can connect an expression pedal and assign it to Volume.
Would it be possible to run from the midi out of the KPA and back into it's midi in and control things like volume pedal levels and such by midi cc? Basically send cc messages to itself?
FYI : that's what the GORDIUS TinyBox does: run MIDI OUT of the KPA to the TinyBox and from there back into the MIDI IN of the KPA. Then a KPA rig or effect change can trigger any combination of extra MIDI messages (CC, SysEx, ...) to the KPA or to other devices connected to KPA MIDI THRU.
Just looked and the KPA only sends PC via midi. It will control CC on things like volume but only if you have an expression hooked to the Remote. Even that way it does not look like you can save that CC value per Performance. No worries. I've checked everywhere and it seems like input volume cannot be controlled per Performance. I know you can lower the rig volume but that does not have the same dynamics as lowering the input volume. I will stick to the flat EQ with the level down as my fix. This thing does everything else so I guess I'll let this one slide. Ha.
I.e. I hope the sarcasm was implied.
if you are using The Remote, you don't need MIDI CC messages. You can use the KPA parameters instead.
Input Volume can be controlled per Performance Slot more than one way. Here are a couple that come to mind -
1) instead of using Rig Volume, turn down the Gain Knob. You can save the Slot that way, or use Morph to control a Slot-specific gain range. If you don't want to use an expression pedal, the Remote Rig/Slot switch can be used to go from an un-morphed to morphed state.
2) if you prefer the sound of lower input settings, Unlock your input settings, and you can save the input settings for each Slot.
FYI : that's what the GORDIUS TinyBox does: run MIDI OUT of the KPA to the TinyBox and from there back into the MIDI IN of the KPA. Then a KPA rig or effect change can trigger any combination of extra MIDI messages (CC, SysEx, ...) to the KPA or to other devices connected to KPA MIDI THRU.
TinyBox4Kemper website
Interesting. I don't see that it's available yet.
if you are using The Remote, you don't need MIDI CC messages. You can use the KPA parameters instead.
Input Volume can be controlled per Performance Slot more than one way. Here are a couple that come to mind -
1) instead of using Rig Volume, turn down the Gain Knob. You can save the Slot that way, or use Morph to control a Slot-specific gain range. If you don't want to use an expression pedal, the Remote Rig/Slot switch can be used to go from an un-morphed to morphed state.
2) if you prefer the sound of lower input settings, Unlock your input settings, and you can save the input settings for each Slot.
Thanks. I find that just lowering the gain does not have the same feel but I will try #2. I did not know this was possible. I've asked several times and you are the first to suggest it. Good to know.
Could you use an eq post stack and have it boosted, then turn it off when you want the volume drop? Just an idea and don't know if it'll work how you want
Lowering the volume in stomp 1 (pre stack) is not the same than post stack. In the first case it will also lower the amount of any distortion which comes after slot 1. Is this intended by you?
Lowering the volume post stack will only lower the overall volume of the rig without affecting the amount of distortion..
Ah ok. 
