[nednednerb]

I'm guessing that each session is MIDI based OR has Elastic Audio turned on for AUDIO tracks.

If that's true, I'm guessing the MIDI is "tick-based" and/or EA audio "warped" onto the tempo BPM of each session.

If you have either MIDI and or AUDIO that you want to import, you need to do one of a few things which will be variably "lossy" in terms of the initial information in the session you import from.

1) Perhaps it's easiest to Save As... Then Select All Tracks, Commit them or Bounce them out to individual stems of audio, which no longer have Elastic warping of any sort, and THEN import those audio stems. Obviously, you lose FX and other edits, but the sound quality will be most faithful to the original, I think.

2) You might also Save As... Then edit the session to make the MIDI and Audio tracks "sample-based" and depending on whether you have any tempo automation (assuming not), then when you import those tracks, the timing might be absolute (sample) instead of tick (tempo). This option is potentially more confusing and prone to issues by my random guess.

Would something like the above work? What is your end goal in terms of not "adjusting length and speed" but putting them in the 'same session' with 'one tempo'?