You're using the wrong function for what you want to do. Slide is intended primarily for MIDI, where sliding is commonly used to shift data by relatively small amounts to compensate for timing issues or to impart "feel." The help menu (click on the "Help" button in the Slide dialog) specifies that the Slide function includes Notes and Controller data, with the option to include Markers as well.
For audio and data encompassing an entire project, you have three options.
1. scook's method is the simplest
2. Choose
Options > Select Envelopes with Clips, select All, and just drag everything over 8 measures.
3. Choose
Options > Select Envelopes with Clips, select All, and use Nudge set for the appropriate number of measures.
There
is an undocumented (i.e., no guarantees) way to use slide with automation data, but only if you're inserting at the beginning of a song and it only functions this way the first time you do it. After that, it won't have the desired results.
1. Select All, then
Process > Slide # of measures.
2. Hit ctrl-Z to undo the slide.
3. Repeat step 1.