I will have to admit it kind of spoils you! The way you can easily lay out your channels any way you want is pretty amazing! Have you used any other racks other than the D-Rack with your SD9? Can you interface with one of the SD-Racks without the need to purchase additional hardware? If I understand correctly, the SD9 has built-I'm MADI ports, but I wasn't sure if they were just for sending out audio for recording, or if there are inputs too.
Yes, the console does spoil you. I love mixing and matching channel types on different banks (layers). I also love the ripple feature for automatically routing consecutive I/O at any number of channels you set. The copy feature is outstanding allowing you to copy one channel or part of a channel very simply to as many or few channels as you want (a quick reset of the console with the eq points where you want them, compressor set up the way you like etc, can be done by setting up one channel and copying it to the rest of the console with about two button pushes). Presets (library functionality) not only save what you want, but you can save groups of channels, say your 10 channels for a drum set, and be recalled to quickly A/B or recall your eq/compression/etc for an entire set of channels. The dynamic eq and fx are absolutely fantastic. You can even make folders for your presets and session files, which is a real plus for people who love to stay organized like me. The list really goes on and on.
But back to your original question, no, I have not used other racks with the SD9. We own two D-racks and they have been great, though less flexible if you want to add a bigger console to your inventory, since you would have to get the LBB or LRB as mentioned. However, the console does have Both Madi In and Madi Out (2 connectors) so it is possible to use it with one other Madi device, whether that be a rack or recorder.
As a side note, Digico is extremely cautious with the cat5e cable specs for the D-Rack. I was planning on installing cable in a couple of buildings since we use the console both outdoors and in multiple buildings on campus. I ran into a lot of fun first of all trying to figure out what Digico would allow and then secondly what would work even if it wasn't "up to spec." Digico's specs include: cable cannot exceed 225ft (75M), cannot have any connections (if installed both sides must be "tails"), must be Shielded cat5e, must have a ferrite core on each end, etc. We have successfully used a homemade 300' shielded cable multiple times without ferrite cores. I also installed connectors that terminate in boxes and we have used cat5e cables on both ends (one to the console and one to the D-Rack) with no ferrite cores for more than 100 hours of use and have had no problems so far. Everything I have done has been with shielded cable though, which is absolutely essential.