The logic of any deal is simple.
Trading Amare would be a disaster. The Suns do not have enough bad contracts to fill in the $8.7 million deal, so it would need means trading KT or Nash. It is absurd.
The Sun can afford to give up Marion and KT (plus picks) for KG without the slightest fear. It gets complicated if the deal has to include other teams (due to questions about Marion), but that's the best case scenrio.
I am not convinced the Suns can afford to give up Barbosa, Bell, or Diaw in that scenerio without suffering on the court. To give up three top rotation guys for one player would leave the Suns with only six rotation guys and no draft picks. Considering that one of the remaining guys is Jones who is very limited and Diaw who is coming off a very disappointing season, giving up Barbosa or Bell could prove fatal on a team without enough real depth already.
The problem is that most Suns fans rightly suspect that Marion, KT, and picks are not enough, but giving up Bell or Barbosa would be too much to survive.