Unfortunately no, you can't time remap both audio and video at the same time. You can right click on the audio and choose Edit in Soundbooth and change the audio speed there. It's not ideal, but it gets the job done.
Hope this helps,
Once you have the Time Remapping done, as required, you can use the CTI (Current Time Indicator w/ the Edit Line) and the Effects Control Panel, to add your Keyframes. As I do not think that one can have two Effects Control Panels open, you would Keyframe either the Video, or the Audio, and then just place the CTI (appears in both the Timeline and the Effects Control Panel's mini-Timeline) over the first Keyframe, and then select the other Clip. The CTI will be where you need it to be, and just add the appropriate Keyframe there. By toggling between the Audio and Video Clips, you can match the position of each. I believe that Time Remapping will "detach" the Audio from the Video, and do not think that Relinking will allow both to be opened in the Effects Control Panel, as you could, with a normally muxed Audio & Video Clip. Just a bit more clicking, but should be easy.
Check me out, that Time Remapping will detach the muxed files, and that Relinking does NOT put them "back together again." If I'm wrong, and it does, then you can have both the Opacity (or similar) in the Video and also the Volume in the Audio.
[Edit] Also, when you have done the Time Remapping for the Video, you can change the TimeCode Display to Audio Units, set the WAB (Work Area Bar) over that Remapped Video Clip, and hover over the little center block in the WAB. That will give you the new Duration, and you can then use that measure in Soundbooth, or Audition, to adjust the Duration of the Audio Clip to match.
Message was edited by: Bill Hunt - Added [Edit]
I'm trying this now too and will provide steps if I figure out a good way to ramp audio with video.
I did not understand or follow Bill's response at all.
You can't ramp audio in Premiere CC 2014 (lame).
I tried Audition. It has has a very convoluted pitch/stretch tool - it didn't make sense/wasn't viable for this purpose.
I was trying to duplicate the ramping the iPhone 6 plus applies to its 240fps clips (when you copy the clips to your computer you lose that ramping).
After Effects is the way to go with "Enable Time Re-mapping", which also applies to the audio. Here's the output for my video Iphone 6 Plus 240fps + Image Stabilization Test - Mountain Bike Drop + Jump - YouTube.
There are tutorials on youtube for this - some of them super long and convoluted, leaving critical steps out. A shorter, good one is here After Effects Tutorial | Ramped Slow Motion - YouTube.
Use the Rate stretch tool on the audio or both the audio and video.