Hi Mike
This should be possible. If you have the non-AS version DMK, the longest exposure is 30 secs I think, and this is more than adequate for auto guiding.
When I use my SBIG ST7 for auto guiding, the guide star exposures range from 2 to 10 secs, although the ST7 is more sensitive (and cooled) than the DMK.
I suspect you would have to use a
GPUSB from Shoestring Astronomy if your EQ6 has an ST4 type auto guider port. I have used the GPUSB with my Orion Deep Space Imager ccd and Craig Stark’s free software
PHD for guiding and this combo works very well indeed.
Have a read of this pdf
article to get an understanding of webcam auto guiding.
WARNING – It is a long, slippery slope and it looks like you are on it. Long exposure auto guided astro photography is obsessive, and expensive!
Cheers
Dennis