A lot of it is going to be trial and error. You may need to find some software that uses the DSI in Mac, but I doubt it. Probably a dual boot system to Windows XP at least, if not a cheap laptop with at least Windows 7 Premium, I think, might be your minimum required system.
As for the focuser, the DSI is an 1 1/4 inch, so you will need to use the 1 1/4 eyepiece unit to hold the DSI. I can't remember where my SN10(LXD55 10") came to focus, but I think you will have to remove the focuser extension tube that is screwed onto the SN8 focuser tube and then screw back on the 1 1/4 eypiece holder.
Please don't get me wrong, but you may get some decent shots with the DSI of galaxies, but nebulas are going to be pretty hard work with the DSI's limited field of view. You are probably better off going to a DSLR or a QHY8.
Also, the LXD75 is not going to be that great for imaging. You can't buy a #909 accessory port module anymore, but some after market ones are out there to plug into the AUX port on the front of the LXD75 control panel, which is your guiding input. This will be required to take a "pretty picture", as you will probably have to guide to get any exposures of decent length.
Light heartedly, you are spiralling into an unfathomable money pit and a steep learning curve, when you consider that you may need another camera, guide scope, cables, attachmnets etc. Then there is polar and drift alignment for accuracy and good guiding.
Having said all that and depressed you, get out there with what you've got, experiment, read, learn. I'm sure some of the more experienced guys will have something to add.
PS: Join a Society near you, and go and see how others do it. Then emulate the successful ones.
