Nope, I wouldn't. If you've got the 300D that will work very well on your LX90 8". You might need a focal reducer, some adapters and other bits and pieces, but it's just what you need.
If you want to do planetary imaging, then get yourself a webcam like the ToUcam 900nc. You'll get the webcam + 1.25" adapter + IR blocking filter for around $250-$300, with spare change left over from what you would've spent on the DSI Pro.
If you want to spend even more on planetary imaging, then you can spend over $1500 on a webcam but if you're just starting out I wouldn't even look at going there until you've cut your teeth with a ToUcam.
Good luck, and don't forget to ask heaps of questions!
btw
to the forum! Where abouts in sydney are you, and how did you hear about us?