I've always made my whipped cream with a 'stick hand blender, which creates the most amazing thick rich whipped cream! I never liked the airy, oily w/c from Starbucks but I wanted to get a dispenser for convenience therefor I bought the Isi pro red... which I hated! It was airy, thin, and melted into 'oil/fat' floating at the top of my Latte. I know I'm using it right because it comes out looking perfect, but the thin, airy consistency is what I hate. Is there a dispenser out there that can dispenser thick, rich w/c that holds its form much longer rather than melting quickly in hot drinks? I returned the Isi Pro dispenser and went back to using my immersion blender
As you already noticed yourself, a siphon and a mixer create different textures of the whipping cream. These textures are a fundamental property of the technique used for whipping, and you cannot do anything to change them.
If you want to have mechanically whipped cream, then you have to whip it mechanically. You cannot turn a siphon into a mixer.
This is not to say that siphons cannot be used to produce stable foams, but then this is a chemical property of the foam and its ingredients (especially the stabilizers used). If all you are making is whipped cream, it will have the whipped-cream-from-siphon consistency.