I would suggest maybe doing half sorghum and half BRS. I recently did 3 LBS of Brown Rice Syrup, 2 LBS of Rice Syrup Solids, and 2 LBS of sorghum and while the bitter taste is not there, you definately get a more pineapple taste (I couldnt exactly make the taste but now that you mention pineapple). When I add raspberry extract to the brew it almost tastes like apricott. Very weird but I think I learned from this batch. I think a couple pounds of malted buckwheat mixed with 2 LBS of BRS, 2 LBS of sorghum would probably make a pretty decent brew. I plan on doing some malting of buckwheat, millet and quinoa in the next few weeks. With a new baby, tax season, and regular life I dont have much time as I want!
I know Darklord and Lcasanova (sorry if I didnt spell those right) have brewed with BRS and I am planning on asking them their opinion on BRS...
But back to stout: I have attempted a stout 3 times now. All times the taste is very good but the darkest it has been is like milk chocolate. I have BURNED 3 lbs of buckwheat, used coffee, and drk chocolate and still just like mud color. I think that if you matled your own buckwheat, millet, quiona or even sorghum and then toasted it to a darker color you would have better success than me. the sorghum syrup is so damn light that it really lightens everything you put it in. I once had my steeping water BLACK and then added sorghum syrup and I was amazed how light it was after adding.