24 bit, 192 KHz is the highest sample rate used for commercial audio.
The audio upconversion on DVD is a plus, but look for a veritable converter.
One that has 48, 96 and 192khz.
Sometimes 96 sounds better than 192. You want to keep your options open.
ps. Above has nothing to do with video.
As for DVD video upconversion. It all depending on your display:
Normal DVD video has a samlpe rate of 480p.
If you have a 1080p or a 720p display. Make sure that the DVD upconversion matches your display.
Display has 1080p. So DVD should upconvert to 1080p.
I you have a 1080p display, but the DVD only upconverts to 720p. That's no biggie. You can do it, you just won't get 1080p.
Hope that helped?