Playing through a passive at a very high setting means the output impedence of the passive is very high - therefore heightening the downsides of a passive. If you really love the passive, then I would look at a power amp with high gain and high input impedence, rather than doubling your investment in the existing amps. Power amps vary considerably in both regards. Tube amps can be best with passives as many have both high gain and high input impedence.
