I understood more or less the claim that $k$-tuply monoidal $n$-categories can be seen as $n$-categories equipped with an action of the $E_k$-operad.
For $k=2$, we have a homotopy equivalence $E_2(r) \cong K(P_r, 1)$, where $P_r$ is the pure braid group on $r$ strands. Let $\mathcal{C}$ be a braided monoidal category, so $E_2$ acts on $\mathcal{C}$. Moreover, we have an action of $P_r$ on objects of the form $V_1 \otimes \dots \otimes V_r \in \mathcal{C}$.
My question is, is there some higher analogue to $P_r$ for $k>2$?
Edit: the answer is basically given in the comments of this question: Braid 2-groups, symmetric 2-groups
However, I would be very happy about a definitive answer in terms of generators and relations of this 2-group. As far as I understood, it should involve the Zamolodchikov Tetrahedron equation.
Edit: I just noticed that I'm actually also interested in $n > 1$ (not just higher $k$), which my previous Edit refers to.