If you want more than DSD 64 or 192kHz 32 bit you can’t use the bridge II which connects via Ethernet. These are the max the bridge II will do.
You will have to use something like a music streamer and connect via USB or I2S to get DSD 128. Does Roon Rock have a USB connection?
From my understanding PSA isn’t doing more development on the bridge II card as they are coming out with a bridge III card. Now it will not support Roon so that doesn’t appear to be an option.
With DSD128 on the Melco (or USB-attached external drive) there are quite some options (i.e. BubbleUPnP) to play it on the DS via USB.
Do you use Minimserver on the Melco instead of Twonky? If not just give it a try. Not that difficult to install providing slightly better SQ and more settings/tweaks. However a small donation would be appreciated, it’s for free…