Blockdiagram with dsp library

Blockdiagram with dsp library

I am using the dsp library, http://www.texample.net/tikz/examples/fir-filter/, to create a blockdiagram. Now I got 2 problems.
I defined two labels, r and d_i however they are not visible on the screenshot because I believe the standalone package cuts down to the current shape (does not see the labels?).
Is anyone capable of changing the plus symbol in the library. I namely want a plus symbol like in matlab or can give a different solution such that I can create e.g.
        -
    -----O-----
        +|
         |
         |_____

code:
\documentclass{standalone}
\usepackage{graphics}
\usepackage{siunitx}
\usepackage{tikz}
\usetikzlibrary{dsp,chains}
\usepackage{pgfplots}
\usepgfplotslibrary{groupplots}
\pgfplotsset{compat=newest}
\pgfplotsset{plot coordinates/math parser=false}

\DeclareMathAlphabet{\mathpzc}{OT1}{pzc}{m}{it}
\newcommand{\z}{\mathpzc{z}}

\begin{document}
\begin{tikzpicture}
    \matrix[row sep=2.5mm, column sep=5mm] {
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        \node[dspnodeopen,dsp/label=above] (m08) {$d_i$};     &
                                              &
                                              &
                                              \\
        %--------------------------------------------------------------------
        \\
        %--------------------------------------------------------------------
        \node[dspnodeopen,dsp/label=left]  (m10) {$r$};       &
        \node[coordinate]                  (m11) {};          &
        \node[dspadder]                    (m12) {};          &
        \node[coordinate,dsp/label=above]  (m13) {$e$};       &
        \node[dspsquare]                   (m14) {$K$};       &
        \node[coordinate]                  (m15) {$u$};       &
        \node[dspsquare]                   (m16) {$T_u$};     &
        \node[coordinate]                  (m17) {};          &
        \node[dspadder]                    (m18) {};          &
        \node[coordinate]                  (m19) {};          &
        \node[dspsquare]                   (m1A) {$G$};       &
        \node[coordinate]                  (m1X) {};          \\
        %--------------------------------------------------------------------
        \\
        %--------------------------------------------------------------------
                                              &
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        \node[coordinate,dsp/label=left]   (m22) {$t$};       &
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        \node[dspsquare]                   (m2A) {$T_y$};     &
        \node[coordinate]