You will need to look at your DLNA Renderer to see what it is receiving, to confirm MC is indeed up-mixing to a Sample Rate of 192 kHz. But it is.
I just played some 44.1 kHz, 16 bit FLAC files to BubbleUPnP running on my Android phone as a DLNA Renderer. I set the DLNA DSP to up-mix to 192 kHz Sample rate. I set the Output Audio Format under "Tools > Options > Media Network > Add or configure DLNA servers > Audio > Format" to "MP3 low bandwidth" and "MP3 high bandwidth", which gave me 64 kbps and 320 kbps bitrate MP3 files respectively. Both formats showed as 192 kHz Sample Rate in BubbleUPnP.
So the DSP is working fine. It is just that MC doesn't show what it is doing in the DSP dialogue under "Tools > Options > Media Network > Add or configure DLNA servers > Advanced > DSP Studio". It would probably be nice if it did, just like it does for local Zones, but it never has.
In the past, I think the reason given for it not showing what it is doing was that MC wasn't using its Audio Engine for playback, so there was nothing to show. But "obviously" there is, as DSP is changing the Sample Rate, and the Audio Format selection is changing the format to whatever is selected. However, DLNA is a file-based process, so what is actually happening is more like a file conversion using the Audio Format and DSP parameters, and then the file is sent to the DLNA Renderer. Hence, look at the Renderer to see what it is receiving.