This isn't really an answer because you probably don't use my sodastream technique. However I am making pineapple soda as probably my last batch before going on to lite ciders instead. To make it palatable I added red flavors to make sort of pineapple blush.
I mail ordered a jug of pineapple syrup which was advertised as 50% real juice but came as 6% with terrible artificial overtones. I am adding some minute maid berry frozen juice concentrate (mostly berry substitutes but at least real fruit based) and a bit of lemon and it's pretty darn good.