Midi Thru and play

This is a request (with a question) for support only. It is not a feature request or a bug. In reviewing related issues and studying Windows audio I have tried to understand this better. My PC API options in Msc. are plentiful from DS to DS- KS, MME and Wasapi. The latter is a God send, I believe, for those of us that have a hardware configuration that has a "default communication device" set-up requiring shared buffering. This has allowed me to mix Fluid with another sampler/library in non-exclusive modes and then send the "mix" to separate audio outs. But not all apps are quite so giving. I frequently get "device allocation" errors occasionally linked with "midi port not open" errors. Frequently "he who sets the audio out, gets both audio outs and sole possession of the buffer." (a sort of winner takes all) If the destination app gets it, the source may respond by refusing to play, greying out its panels and so forth. This has led me to think that I must have a "callback" from the port in order for the virtual midi drivers to work. But I am unclear as to which app in a two app set-up gains priority except in so far as he who opens and calls first seems to be in a position of advantage. Some seem to require that their own internal synth receive it. But this is a mistake on many home PC's running on slightly different home hardware configurations because there is just not enough room for more than one.

My question; In Musescore, will Midi go "thru" and will start, stop .rewind, speed, and loop commands generally be enabled if the synthesiser is disabled?