Advice on installing split system with existing evap cooling

I would like to get some advice on my options for installing a split system aircon in a room that already has existing evap cooling.

I have recently converted a room into an enclosed theatre room, and wish to keep the cooling independent from the rest of the house. The house has evap cooling and ducted heating throughout. Having windows and doors open in the theatre rooms defeats the purpose of dark and soundproof room, so evap cooling is not a good option.

What I am thinking of doing is installing a split system in that room, but I am unsure of what to do with the evap. A few scenarios that come to mind are:

1 - leave the duct and vent as is (close the vents)
2 - remove the ductwork and seal off the vent from behind (leave vent in place)
3 - remove the ductwork and the vent (re-plaster and re-paint)

Option 1 is most favourable and the easiest. I want to avoid Option 3, as I have only recently completed a whole room re-paint and do-up job in the room and don't want to go through that all again.

But if I were to leave everything as is but close the vent, what would happen if both were to be run at the same time (the rest of the house is needs to cool down via evap)? I also am cautious about the excess moisture that will be introduced into the closed theatre room. With the vents closed, would the moist air get trapped in the ducts and build up mould? Would moist air still seep through the vent gaps and into the room?

I'm especially concerned about humidity and mould since our last place had a major untreated moisture problem. We don't want to go through that again.

Your advice is much appreciated. Thanks!