Jeff,
This is just from my research online (my solana is sitting empty in my dining room, not set up yet). I have seen people use DSB's in their tank, some people have used the second chamber in the back as a fuge with a daylight bulb to grow some macro, and also... you can put in a new skimmer. I have seen threads of people using many different ones (tunze, deltec, precision marine). I have a tunze auto top off I'm going to use, putting a 2.5 gallon freshwater tank in the stand. Also, you could hang a phosban reactor off the back and put carbon or other media in it. I think you could get away with all the equipment you'd want, without an external sump, that’s just my opinion from seeing other peoples work.
Neil