A couple of things to consider on those solid state relays, You probably want ones designed to switch a DC load and you are going to have to meet the minimum load current.
All of the solid state relays I have used that are designed to switch an AC load will latch on once the control voltage goes up enough. They will switch off when the load current goes through zero on an AC load. If you are using them to control a signal into a computer, it will probably be a DC signal, so it will not switch off, even if the AC control signal goes away.
Another standard feature of solid state relays is that they have a minimum load current to switch on at all. I think it is related to how the load side of the optical isolation is powered. Driving a control signal into a computer input port probably will not provide that load. A pilot light probably would be enough, but look at the data sheet on the relay for sure.