Audio levels changing when put in multitrack

The scale on the left simply indicates how much additional level you've either added or subtracted from the channel level - it's just like the calibration scale on any hardware mixer. The scale on the right is the actual meter scale - that's why the calibrations reach right over to the edge of it.

Balancing audio levels has nothing to do with meters -that's all down to your ears. Because Audition uses Floating Point mixing with effectively no distortion ceiling, the absolute levels don't matter very much, as long as you keep them within reasonable bounds. What this means in practical terms is that even with the meters banging into the red, and your monitoring sounding a bit distorted, you can get the correct levels back whin you mix down to a file that opens in Waveform view, simply by normalizing it so that the peaks sit at 0dB (or slightly lower). The signals will be scaled back to the 'correct' levels. Yes I realise that this sounds like a bit of magic, but it's a direct consequence of the Floating Point maths involved in the audio engine. What it means is that Audition's mixer has a ludicrous dynamic range, extending up to somewhere around +1500dB - no, that is not a typo. So you can have a mix that opens in Waveform view as a solid block of green, and normalize it back to stop at 0dB without any difficulty or loss at all.

And ultimately, that's why none of the level discrepencies you think you're seeing in Multitrack matter in the slightest - you can't overload the system, and even if everything's too quiet you can boost it without loss. Loads of people make a fuss about it, but it's all for nothing! The only reason that a really hot mix sounds distorted is because your sound device lives in the real world, and has to deal with a fixed number of bits, and it's perfectly possible to overload this. But like I said, it really doesn't matter, because you can correct this afterwards.