using cplex as a subsolver of bonmin and couenne

in Couenne's case, it depends on how you have downloaded it. If you
downloaded the binary distribution, I'm afraid Cplex is not supported
as an LP solver (and Clp will be used instead).

However, if you have downloaded the source using Subversion, you
should be able to have Couenne use Cplex by:

1) configuring it with the options

--with-cplex-incdir=/path/to/

cplex/includes
--with-cplex-lib="/path/to/cplex/libraries -lpthread"

2) specifying the option

lp_solver cplex

in the option file couenne.opt.