You could take a look at my poor man's sd backup loader in the tutorial section. Some things are described like the load time the first time with a modmii nand.
Connect your sd card to a pc and look at the number of free bytes. Put a small text file on the sd card and read the number of free bytes again.
Tell us the difference between both numbers.
Try to get sneek running first without font.bin and di.bin in your sneek folder. If that works, you know your emulated nand is working fine.
After that, you can add di.bin and font.bin.
While sdhc cards should work fine, I also had issues when I tried to boot neek with bootmii installed as boot 2.
The same card worked fine if I launched neek from the hbc channel. (card out, start wii, card back in, HBC and launch bootmii..)
DML requires sneek to be launched from the bootmii as boot2, so that won't work this way.
You can try a bootmii nand backup as emulated nand. Extract it with showmiiwads / showmiinand.
If you interrupt the first boot of a modmii nand, than you need to copy the nand folders over to the sd card again.
Do you still see one or more lightflashes on your drive slot?