Hi Mikael,
If your DAC doesn’t accept DSD files then upsampling in HQP to DSD won’t enable it to do so. You are correct that upsampling to the highest supported PCM resolution of 384 kHz is the most that can be done.
KMan has set out what works for him with the Deckard DAC, and you can try each of the resolutions listed by him as outputs from HQP to see if any of them are better for you than others. Sometimes a DAC will have a simpler time dealing with lower resolutions than it’s maximum and there could be an SQ sweet spot. Still worth starting with highest res though.
It is quite possible that after listening to the settings as per KMan’s post, you find that you don’t hear any audible benefit. That may be because the DAC is doing a pretty good job of upsampling itself, or because other components in your system are masking any difference, or simply because the benefits from upsampling in HQP are not the kinds of thing that are significant for you when listening to music. I started a thread about how HQP may not be for everyone and I haven’t changed my views about that.
Lastly, HQP can happily run alongside Roon Server. That is what I do on a Gigabyte BRIX. Roon Server is a Roon Core. You configure the Core using another installation of Roon on a computer (Remote) or a tablet. Point Roon Server at localhost if HQP is running on the same computer as Roon Server.