The Cnat should be able to remove 6K scratches. I've used mine for everything down to 1K.

Try making a medium to thin slurry on the Cnat. Hone with the slurry on there, and dilute it down to almost pure water. That will expedite removal of and left over scratches. Once you're done with that, wash the stone and do a few laps with pure water until you're satisfied. Using the slurry stone will also burnish your stone and make it finer. So it's kind of a win/win.

Make sure the edges of the slurry stone are rounded - lessens the chance of rolling it and scratching up your nice flat hone. I tend to think that a smoother/more burnished stone creates a sharper edge. It also slows cutting speed, so there's a bit of a trade off.

Diagonal scratches are good, what you don't want to see is scratches running up and down the blade. The ones in the third picture look a bit deep though, more like 1K scratches that weren't quite removed by the 6K stone. You might also consider backing down to the 6K to do a little more work on it, then moving on to the Cnat.