  We study the Replica Symmetric region of general multi-species
Sherrington-Kirkpatrick (MSK) Model and answer some of the questions raised in
Ann.~Probab.~43~(2015), no.~6, 3494--3513, where the author proved the Parisi
formula under \emph{positive-definite} assumption on the disorder covariance
matrix $\Delta^2$.
  First, we prove exponential overlap concentration at high temperature for
both \indf~and \emph{positive-definite} $\Delta^2$ MSK model. We also prove a
central limit theorem for the free energy using overlap concentration.
Furthermore, in the zero external field case, we use a quadratic coupling
argument to prove overlap concentration up to $\beta_c$, which is expected to
be the critical inverse temperature. The argument holds for both
\emph{positive-definite} and emph{indefinite} $\Delta^2$, and $\beta_c$ has the
same expression in two different cases.
  Second, we develop a species-wise cavity approach to study the overlap
fluctuation, and the asymptotic variance-covariance matrix of overlap is
obtained as the solution to a matrix-valued linear system. The asymptotic
variance also suggests the de Almeida--Thouless (AT) line condition from the
Replica Symmetry (RS) side. Our species-wise cavity approach does not require
the positive-definiteness of $\Delta^2$. However, it seems that the AT line
conditions in \emph{positive-definite} and \emph{indefinite} cases are
different.
  Finally, in the case of \emph{positive-definite} $\Delta^2$, we prove that
above the AT line, the MSK model is in Replica Symmetry Breaking phase under
some natural assumption. This generalizes the results of J.~Stat.~Phys.~174
(2019), no.~2, 333--350, from 2-species to general species.
