  In these notes we prove two main results:
  1) It is well-known that two strongly continuous $E_0$-semigroups on $B(H)$
can be paired if and only if they have anti-isomorphic Arveson systems. For a
new notion of pairing (which coincides only for $B(H)$ with the existing one),
we show: For a von Neumann algebra $B$, a strongly continuous $E_0$-semigroup
on $B$ and a strongly continuous $E_0$-semigroup on $B'$ can be paired if and
only if their product systems are commutants of each other.
  2) On the way to prove the former, en passant we have to fill in a long
standing important gap in the theory of intertwiner product systems \`a la
Arveson (known, so far, only for $B(H)$ in the separable case): Intertwiner
product systems of faithful strongly continuous $E_0$-semigroups on von Neumann
algebras have sufficiently many strongly continuous sections.
  Both results are out of reach for Arveson's methods [Arv89,Arv90] (which work
only in the case $B(H)$; see Remark 1.6, especially, Footnote (f)) and based on
the alternative approach from Skeide [Ske16].
