  We report a comparative study of the specific heat, electrical resistivity
and thermal conductivity of the quasi-two-dimensional purple bronzes
Na$_{0.9}$Mo$_6$O$_{17}$ and K$_{0.9}$Mo$_6$O$_{17}$, with special emphasis on
the behavior near their respective charge-density-wave transition temperatures
$T_P$. The contrasting behavior of both the transport and the thermodynamic
properties near $T_P$ is argued to arise predominantly from the different
levels of intrinsic disorder in the two systems. A significant proportion of
the enhancement of the thermal conductivity above $T_P$ in
Na$_{0.9}$Mo$_6$O$_{17}$, and to a lesser extent in K$_{0.9}$Mo$_6$O$_{17}$, is
attributed to the emergence of phason excitations.
