If an adjustment of pH must be made, be careful using sulfur that you get the right instructions for you soil or mix on how much to add. Doesn't take much to lower the pH of sandy soil.

I would submit a sample of the entire mix I plan to use for analysis and specific instructions on amendments needed.

Like Drew said check the PH. I do disagree about sand being low in PH....sand, silica can't be diluted in water so would have no PH so would be neutral PH. Things in the sand mix could lower or raise the PH so without a test you would not know.

I think spruce bark would be fine to use but bear in mind what Drew said bark FINES. You need the right particle size. Big pine/spruce nuggets won't do it.

I live in Florida and the entire state is just one big sand bar. Grow almost 200 BB bushes and they like sand just fine as long as it has a lot of organic material mixed in to hold moisture around the roots.

On the sand here in MI on the west side we grow the most Northern High Bush than any other state, and it is because the rain has made the sand acidic. What's great about sand is it is so easy to change the PH! Clay pretty much will always remain alkaline, why many don't even try to grow blueberries in it. That evidence is all over the net, and is why I said sand is usually acidic in nature.
But you could have building materials such as lime in your sand, you need a PH test.
Here's an article from Michigan State University that backs my claims. I will never state anything without some evidence. A great series of articles here on PH and organic matter too.