So I would be able to CREATE "192khz-sound" and also RENDER it in 192khz quality BUT because of the bad soundcard I would always HEAR a worse interpretation/output of the actual higher quality sound.

Correct.
 
Data would have to be down-sampled to whatever your interface can support, so if the best it can do is 48KHz then that's what you will hear through your speakers or headphones.
 
Whether or not you could actually HEAR the difference is another matter. In all likelihood, you will not.

Unless you are recording very high frequencies that are inaudible to humans for some reason, 192kHz is only better for certain types of audio processing, not for recording/playback.
 
Almost all objective evidence shows no benefit in going above 44.1 or 48kHz for playback of music and there is quite certainly no benefit to going above 96kHz.

How do you know your synth plugins can produce any audio high enough to make 192KHz even relevant in the first place? That would mean them producing audio output up to around 96KHz.

So it's not like you or anyone else can actually hear it. Or even find speakers or headphones that can output that kind of frequency.