Robust equation numbering

Question

Is there a robust equation-numbering environment
in which I can:

• Have as many columns as I would like (default centered, like a matrix).
• Mark start and end of line(s) I would like numbered.
• Center the numbering across multiple lines which were group numbered.
• Use multicolumn / multirow wherever.

Actual MWE:

\documentclass{scrreprt}
\usepackage{amsmath}

\begin{document}

\begin{gather}
\begin{array}{ccccccccccccc}
K_{\ddot{\phi}}
& \cdot 
\begin{bmatrix}
\ddot{\phi}_{x}\\
\ddot{\phi}_{y}\\
\end{bmatrix}
& + &
K_{\dot{\phi}} 
& \cdot 
\begin{bmatrix}
\dot{\phi}_{x}\\
\dot{\phi}_{y}\\
\end{bmatrix}
& + &
K_{\phi}
& \cdot 
\begin{bmatrix}
\phi_{x}\\
\phi_{y}\\
\end{bmatrix}
& = &
K_{v}
& \cdot
\begin{bmatrix}
v_{mtr.l}\\
v_{mtr.r}\\
\end{bmatrix}
%%
\\[+2em]
%%
I
& \cdot
\begin{bmatrix}
\ddot{\phi}_{x}\\
\ddot{\phi}_{y}\\
\end{bmatrix}
& = &
-K_{\ddot{\phi}}^{-1}
\cdot 
K_{\dot{\phi}} 
& \cdot 
\begin{bmatrix}
\dot{\phi}_{x}\\
\dot{\phi}_{y}\\
\end{bmatrix}
& + &
-K_{\ddot{\phi}}^{-1}
\cdot 
K_{\phi}
& \cdot 
\begin{bmatrix}
\phi_{x}\\
\phi_{y}\\
\end{bmatrix}
& + &
K_{\ddot{\phi}}^{-1}
\cdot 
K_{v}
& \cdot
\begin{bmatrix}
v_{mtr.l}\\
v_{mtr.r}\\
\end{bmatrix}
\end{array}
%%
\end{gather}

\end{document}

This MWE does not encapsulate all requested features,
but, for example, I would have liked to have centered all depicted vectors.

Desired Example:

\begin{Equation}
%%
\begin{numbered}
\label{EQN:A}
y & = & m \cdot x
\end{numbered}
%%
\\
%%
y & = & m & \cdot & x
%%
\\
\begin{numbered}
\label{EQN:B}
%%
y & = & M & \cdot & x
%%
\\
%%
Y & = & M & \cdot & X
%%
\end{numbered}
%%
\end{Equation}

(Sorry for the lack of originality in the example.)

Effectively, the Equation environment would allow
the entire list of equations to act as a matrix* or tabular,
and the nested enviroment numbered would encapsulate numbering,
without disrupting the indexing of the matrix.

Answer 1

array is designed for matrices (like the AMS bmatrix that you are using) it is unsuitable for setting displayed equations as it puts the cells in textstyle and the spacing is incorrect. Also if the array only have one row then the ccc doesn't really centre anything, lll would have the same effect, as the cell is just as wide as its content.

example from the updated question

For the updated example you could use alignat rather than gather but the alignment here, aligning = with + seems very strange and designed to imply a symmetry that is not in the underlying mathematics.

\documentclass{scrreprt}
\usepackage{amsmath}

\begin{document}

\begin{alignat}{7}
K_{\ddot{\phi}}
\cdot 
\begin{bmatrix}
\ddot{\phi}_{x}\\
\ddot{\phi}_{y}\\
\end{bmatrix}
&+
K_{\dot{\phi}} 
&\cdot 
\begin{bmatrix}
\dot{\phi}_{x}\\
\dot{\phi}_{y}\\
\end{bmatrix}
& + 
K_{\phi}
&\cdot 
\begin{bmatrix}
\phi_{x}\\
\phi_{y}\\
\end{bmatrix}
& = 
K_{v}
\cdot
&\begin{bmatrix}
v_{mtr.l}\\
v_{mtr.r}\\
\end{bmatrix}
%%
\\[+2em]
%%
I
\cdot
\begin{bmatrix}
\ddot{\phi}_{x}\\
\ddot{\phi}_{y}\\
\end{bmatrix}
&1= 
-K_{\ddot{\phi}}^{-1}
\cdot 
K_{\dot{\phi}} 
&\cdot 
\begin{bmatrix}
\dot{\phi}_{x}\\
\dot{\phi}_{y}\\
\end{bmatrix}
& + 
-K_{\ddot{\phi}}^{-1}
&\cdot 
K_{\phi}
\cdot 
\begin{bmatrix}
\phi_{x}\\
\phi_{y}\\
\end{bmatrix}
& + 
K_{\ddot{\phi}}^{-1}
\cdot 
K_{v}
&\cdot
\begin{bmatrix}
v_{mtr.l}\\
v_{mtr.r}\\
\end{bmatrix}
%%
\end{alignat}

\end{document}

---

original example

For a setting such as the example I would use gather that does centre the expressions and set them in display math mode.

\documentclass{scrreprt}
\usepackage{amsmath}

\begin{document}

\begin{gather}
K_{\ddot{\phi}} 
\cdot 
\begin{bmatrix}
\ddot{\phi}_{x}\\
\ddot{\phi}_{y}\\
\end{bmatrix}
 + 
K_{\dot{\phi}} 
\cdot 
\begin{bmatrix}
\dot{\phi}_{x}\\
\dot{\phi}_{y}\\
\end{bmatrix}
 + 
K_{\phi}
\cdot 
\begin{bmatrix}
\phi_{x}\\
\phi_{y}\\
\end{bmatrix}
 = 
K_{v}
\cdot
\begin{bmatrix}
v_{mtr.l}\\
v_{mtr.r}\\
\end{bmatrix}
\\[+1em]
%%
\begin{bmatrix}
\ddot{\phi}_{x}\\
\ddot{\phi}_{y}\\
\end{bmatrix}
 = 
-K_{\ddot{\phi}}^{-1}
\cdot 
K_{\dot{\phi}} 
\cdot 
\begin{bmatrix}
\dot{\phi}_{x}\\
\dot{\phi}_{y}\\
\end{bmatrix}
 + 
-K_{\ddot{\phi}}^{-1}
\cdot 
K_{\phi}
\cdot 
\begin{bmatrix}
\phi_{x}\\
\phi_{y}\\
\end{bmatrix}
 + 
K_{\ddot{\phi}}^{-1}
\cdot 
K_{v}
\cdot
\begin{bmatrix}
v_{mtr.l}\\
v_{mtr.r}\\
\end{bmatrix}
\end{gather}

\end{document}