Making ice cream on SBD is very tricky! First of all, you need a heavy-duty IC maker. Ours is partly plastic and broke when we tried making our fourth batch.
We found that adding peanut butter to the mix made for the best ice cream...it's an SBD-safe fat and made for a much better texture. Splenda freezes very hard, so without the fat to help, you end up with a rock.
That said, there are other options. I'd try making a SF sweetened condensed milk and try that with recipes that call for sweetened condensed milk (search the net for one called "Jo's sweetened condensed milk"...I've used it before and it works very well in baking recipes). We had some success using SF pudding mixes. Try using a small bit of whole milk, or at least 2% milk. Try mixing Splenda and Stevia or Splenda and Erithrytol (you can buy it at www.netrition.com
if you can't find it elsewhere) or even Splenda plus a SF syrup to try to make it less hard.
Let me know what you figure out...we finally got a new part for our IC maker and are ready to try again. I'm going to try one made with buttermilk, I think, to see what that might do...