Okay, just was interested to see if you ever heard that was possible or not.  I'm imagining a material reacting to music, and imagining that this reaction-parameter was being recorded by the Seq Recorder. 
As far as why, given that you can key, well that's just me - I am lazy and looking for a shortcut!

I am not thinking of iClone driving material changes in UE4 through LLink, although that is interesting that you mention that.  But I think with iClone-LL-UE4 materials are detached, right? 
I'm thinking a change in diffuse-color, or roughness, of a material in iClone won't, through LLink, then adjust the color or roughness of the corresponding material in UE4.

For Audio Reacting you can use a blueprint by "Arthur......"  it records peaks of Bass -Mids -Treble to keyframes.
You can use this keyframes to react to anything that is controlled by keyframes via copy and paste.

I did it with lights only....

Oh Cool...I will be checking that out.  

Here is my Tutorial & the BP to download ... scroll down a bit .....

https://forum.reallusion.com/419325/Tips-Tricks-for-Unreal-Engine-4?PageIndex=125

Thanks Bassline.  

You know what is another weird thing, the LLink skeleton vs FBX skeleton.  I wonder if they are the same.

1) I create Avatar A.in CC3

LLink
2a) Bring Avatar A into iClone
3a) LLink Avatar A to UE 4.26
4a) Avatar A now in 4.26 with "Skeleton A"

Also:

FBX Export to Maya
2b) Export Avatar A from CC3 to Maya, with UE4 profile
3b) Following Smooth, export from Maya to UE4.26
4b) Attempt to assign Skeleton A (from 4a) to this import, and UE4 gives me an error that the bones do not match...
5b) import with its own Skeleton, but this new skeleton now does not match the Skelton A created by LLink, so no animations created for the LLink Avatar work on the imported FBX avatar, nor will it be recognized by a LLink avatar corresponding to its name. 

Best working way is to import from Maya into UE4 with new Skeleton , then select the Maya Character in the Content Folder and go to "IClone Live Link" (above) and select "Create BB for selected Character".
Add the Maya Character into the scene "under the Iclone Origin" , tick the Live Link Button in IClone and go to UE4 Character Details / Live Link / Name .... give it the Name of your Character in IClone....
...works very well....

Hi Bassline303, I am a little confused about the Maya smoothing procedure. In an earlier post you showed that you used rubber band to separate the mouth from the rest of the character and then smooth subdivide (to get rid of bubble gum mouth effect). In another post you mention that there is a weight painting problem with the mouth and that has to be addressed by hand painting (I'm going by memory here, so I may be wrong with the terminology). Could you please clarify if you are able to get the mouth to work correctly after smoothing, and if so what are the steps involved (only selecting, or is there some weight painting)? 

1. To exclude the lips from smoothing works.
2. If you don't want to exclude the lips , you have to skin weight repair the lips...

Thank you so much!

Just further, weight painting was brought up after the fact as a 2nd potential remedy, but he had already discovered that excluding the lip polygon faces from the smoothing procedure would work alone. 

LOL - Sounds like doctors talking about an ill patient:

"Doctor Bassline, there is something wrong with the patient's skeleton..."
"Doctor Bassline, patient presents having an issue with their lips and mouth..."