You are correct I have a mk2 player, so I can't say for sure whether or not the mk1 player application would support 4 drives, I do however think it very unlikely.

I couldn't get those first adapters to work with 2 cards on a PC either so i don't think it's empeg related.

The alternative link I provided was wrong (sorry) it should have been http://linitx.com/viewproduct.php?prodid=11677 a different dual CF adapter, I have 2 of them hence the 4 cards.

I think I should reiterate here that you can't just plug two of these adapters into a mk2 player and expect them to work, I've had to modify each adapter ( cut a couple of tracks and patch in some logic gates) as well as modifying the kernel and hacking the root file system a little to make all this work.