  Let $R$ and $S$ be rings, $C= {}_SC_R$ a (faithfully) semidualizing bimodule,
and $n$ a positive integer or $n=\infty$. In this paper, we introduce the
concepts of $C$-$fp_n$-injective $R$-modules and $C$-$fp_n$-flat $S$-modules as
a common generalization of some known modules such as $C$-$FP_{n}$-injective
(resp. $C$-weak injective) $R$-modules and $C$-$FP_{n}$-flat (resp. $C$-weak
flat) $S$-modules. Then we investigate $C$-$fp_{n}$-injective and
$C$-$fp_{n}$-flat dimensions of modules, where the classes of these modules,
namely $Cfp_nI(R)_{\leq k}$ and $Cfp_nF(S)_{\leq k}$, respectively. We study
Foxby equivalence relative to these classes, and also the existence of
$Cfp_nI(R)_{\leq k}$ and $Cfp_nF(S)_{\leq k}$ preenvelopes and covers. Finally,
we study the exchange properties of these classes, as well as preenvelopes
(resp. precovers) and Foxby equivalence, under almost excellent extensions of
rings.
