Hmmm. This is an interesting question. Can you hone a razor on just the 8K? I suppose you could.

You're likely to have better luck with the Dovo. The eBay special will take a very, very, very long time to hone up on just the 8K.

You might want to consider buying a less expensive 4K waterstone from Woodcraft.com or some of the other sources out there. For less than $30 you could probably get a second stone that would make life a lot easier.

To hone an eBay special on just the 8K you'd probably need to do thousands of strokes, so it's no surprise that you're not seeing much progress. You might try using 1K sandpaper to reset the bevel, then going to 2K sandpaper to give it some polish before going to the 8K. My experience with sandpaper, though, is that it rounds the bevel, which means you need to spend quite a bit of time honing on a 1K or 4K hone to get it flattened out again.

The option I'd recommend is sending it out for an initial honing, then using the 8K for touchups.

Good luck,
Josh