UR44 Newbie Questions

I bought a UR44 for my wife a couple of years ago but never got to using it till now. I want to use UR44 to record some Karaoke based singing. What I am thinking is piping the music on Line in (Channels 5 & 6) and connecting Mics on Input 1 and 2.

I am using windows 10 and I can see all 6 channels in dspMixFx, however when I connect Cubase LE 10.5 it only gives options for 4 channels for mapping, not channels 5 and 6. As such am still not comfortable with Cubase so was hoping that I can use Audacity but have not been able to get Audacity to work. I was thinking Audacity will have 6 channels as Input but I only see option for 1 or 2 channels and even in that I am not seeing any signal.

Does anyone know of any tutorial to get me started?

Thanks

Hi
Regardless of which DAW you want to use I would suggest Youtube for a primer, and in Cubase specifically you will need to set up all the inputs and outputs (in the studio menu), for better help regarding Cubase I recommend the Cubase forum.
On your soudcard you have a feature called loopback, and this is likely the thing you will need to make your karaoke setup work.
Good luck!