Hi Frank,
The images I posted were using the DSI IIIc, so I don't have the extra filter section that you have on the Pro version. Just guessing here, but the extra distance between the focal reducer and CCD may be a problem (unless you've got a modified face on the DSI), and I've seen several posts recommending camera mods to minimise this distance. I couldn't really get the distance between focal reducer and CCD close enough with the "c" variant in order to get reasonable pictures, so think you'll struggle to do any better with the "pro". Personally, I've given up with the F3.3 reducer when using the DSI III. and for other reasons researching my way to finding the best 1.25" (possibly 2" too) focal reducer that is compatible with the DSI IIIc (with an electric focuser on the back of the LX-90, there's no room to accommodate the DSI & focal reducer when mounted via SCT arrangements). I've posted some pictures taken with a "cheap" Astro Engineering 1.25" FR at different FR-CCD separations if you're interested? Having said this, wouldn't have thought you'd run out of focus range, but then I've got no experience with the LX-200 (focus range is huge on the LX-90).
Anyway, one other big tip is to use a focussing screen/Hartman mask, see here: http://www.cloudynights.com/item.php?item_id=518 (however would recommend using equilateral triangles rather than circular cut-outs). These really make life more simple when it comes to focussing...
Hope this helps,
Jon
8" Mead LX-90 + DSI III
Isle of Wight