I would also be interested to hear if you try out the concentrates you mentioned.
I'm enjoying this one as we speak:
1/4 cup Da Fruta Passionfruit Concentrate
4 packets True Lime (~juice of 1/2 lime)
70g Turbinado sugar
18oz water
The Da Fruta concentrate recommends a 1:7 dilution with water. This is a little less than that, but with some lime to make up the difference. I think the sweetness is spot-on. I don't get any of the lime. This is basically like drinking sweetened, carbonated passion fruit juice. And there's not a damn thing wrong with that.
Next time, I will up the ratio of lime to passionfruit. I will try to get some real limes and include the zest as well. Drinking this, I think passionfruit lemonade would be amazing. If you like passionfruit, I highly recommend picking up some Da Fruta concentrate and playing around with it yourself. The flavor isn't quite as intense as fresh fruit, but I couldn't imagine dealing with the real deal in any quantity. They run me 3 bucks a pop, and you maybe get an ounce of juice from them.
I feel like I'm really starting to hit my stride with the soda thing. I'm finally getting a handle on the carbonation. And I've found a reliable sweetness level (120g per liter in an acidic beverage, to my tastes). It's getting really fun and easy to crank out a batch. I think I'm going to spring for a few extra carb caps so I can start bringing 20oz bottles to work for lunch, and keep a pipeline of a few batches going.
I have this laying around from IKEA, so something blueberry-lemony is probably up next:
http://www.ikea.com/us/en/catalog/products/10296015/I haven't tried the blueberry yet, but the lingonberry one is pretty nice.