Looks like Fred has you sorted Nigel.
The DBK means Bayer matrix or Colour. The DMK means Monochrome (no Colour).
Because the Monochrome has no Bayer matrix (red, green, blue) lenses in front of the sensor, it is inherently more sensitive and provides more resolution as each pixel is capturing the same information. Match this with a set of RGB filters and you can get higher resolution pictures of planets etc, in colour which are higher quality than One shot colour Bayered CCDs, it just is a bit more expensive and requires a filter wheel and filters and more time to get an colour image than simply pointing and clicking with a colour camera.
The money you are saving on that excellent DMK from Fred could go towards a filter wheel and filters if you decide to make colour shots, however, monochrome are quite acceptable and show some excellent details on planets and the moon (the latter is pretty much grey anyway)
Through a 12 inch scope you will be getting seriously good details on Jupiter with a DMK depending on the seeing in the atmosphere, so it will be interesting to see what you can come up with.
Cheers
Chris