Impossible to achieve. The very attempt of appearing neutral could be considered a provocative act. A warrior race is quite likely to consider a lack of weapons on display as a sign of weakness and attack, for example.
Definitely not impossible.
You need to think of it outside any cultural context.
In other words what would a rock do when it meets a new alien ?
Be that rock.
Do the things that make logical sense and have no possibility of misinterpretation by a being that can perceive them through whatever perceptive channels it may possess.
That means no shaking hands, no saying hello, no war cries, nothing.
The only real way to achieve a sensible first contact is to do it via mathematics. It's currently the one universal we're aware of.
Then a common mode of communication can be established and appropriate contextual information for the physical contact can be exchanged before the face to whatever meeting.
It may take some time to establish a common understanding of things like the speed of light, basic atomic masses, rules of logic and arithmetic etc... but so what. We have the time.
The
Voyager Golden Disk is a Tour-de-Force in this matter. As is the
Arecibo message.
Basically being your big hero warrior self in a face to whatever first contact situation is a sure-fire way to have a big misunderstanding and potentially start a conflict.
If we've already thought of this, first contact protocols are available all over the web, then you can be sure that species that are far more advanced than us, even if they are warrior dominated, will have thought of them too.
They're clearly not idiots because they achieved space flight. For that they need to know mathematics, engineering and how to manipulate matter. They will have these regardless of any social construction or species taxonomical configuration.
So they can talk in a language we can understand and we can talk back to them.