Forgive me if this was asked already (with 940 posts here I'm guessing it was) but what is Colorado looking for exactly? I feel like their biggest problem is depth, and obviously trading Duchene opens up another spot, but it feels like a "get as many quality pieces as you can" situation instead of making a one-for-one trade.
Isles REALLY don't want to trade Barzal and can still offer a very good package (top four D, top six forward, any first rounder). So, something like... one of Nelson and Strome, one of de Haan/Hamonic (although Hammer's value is higher), and a first. I'm guessing that isn't really appealing to Sakic though.
Colorado is reportedly asking for a high price, but I believe that is largely due to the fact that they have no immediate pressure to trade him. They are trying to address defensive issues by adding a younger defenseman or defensive prospects. The defenseman (younger under age 25) or defensive prospects will be the key to any deal.
The Avs are probably looking at reallocating resources to balance their future lineup.
They have Duchene and MacKinnon at center, but they also have Tyson Jost (2016 - 10th overall selection), JT Compher (2013 - 35th overall selection), and JC Beaudin (2015 - 71st overall) all coming up shortly at center. The Avs likely will select a forward with their top-five selection in this upcoming draft as that is where the value is at the moment.
This same rationale applies to Landeskog, as the Avs have Rantanen (2015 - 10th overall selection) and AJ Greer (2015 - 39th overall selection, ready to contribute in a top-6 role as power forward types.
Quantity, particularly forward pieces, are unlikely to be as attractive to the Avs if they pull the trigger on a Duchene/Landeskog trade.