nice work raymo.
when using my goto dob with dslr i only go to 20 seconds @ iso 3200, i found it gives a reasonable balance and can give good results on the medium to brighter DSOs. the only additional frames i took were darks, as you know how to take them it is worth adding them in DSS (you don't need to do it in another program). after you select the subs, all you need to do is 'select dark frames' from the menu on the left and select the files that they are DSS takes care of the rest. they definitely make an improvement on the image.
http://www.flickr.com/photos/80336656@N07
good job, keep at it, some more subs and darks will make a massive improvement. I'm amazed you could get that result from the image manipulation tools in DSS! I find it really slows down my computer and makes it really impossible to see the changes in 'real time.'
all the best,
Rusty