For an improvement, in my opinion, one has to use Linkwitz-Riley filters for perfect band separation: the frequency roll-off of those filters is perfect in the sense that the roll-off of a certain band, when summed up with the roll-off of adjacent band, doesn't emphasize nor attenuate the signal. (For a graphical explanation, please refer to this picture. "LR" stands for "Linkwitz-Riley".) Also, I believe that common multiband compressors use exactly this filter type, as do certain audio speakers, for audio crossover between the woofer, mid-range and tweeter.

By using Christian-W. Budde's Dual Linkwitz-Riley Filters VST I achieved just that: I separated the signal to Low, Mid and High bands and connected Compressors to each one, which in turn can be sidechained.

For example, this 3-Band Sidechain Compressor can be used for attenuating the bass line so that it doesn't clash with the kick drum too much.

Thanks to Jason Timothy for the initial idea!

Download it here. (Requires Ableton v8.1.1!)

Click.