Yah, you can lay the mulch down really thick. I use tree trimmer mulch at a thickness of about a foot. It lasts roughly a 18 months.
You can actually go really heavy with the tiger 90 for "most" plants. Annonas seem to be very sensitive to it, so be extra careful around them. I applied about 1 ton (2,000 pounds) of tiger 90 to a 1/4 acre as an experiment about a year ago. Out of about 3 dozen trees, the only ones that were adversely affected were a handful of annonas and a guava tree.
While you can't feasibly modify the PH of soil that is > 1% calcium carbonate, it's generally possible to acidify the top few inches of soil above the hardpan.
Organic matter (eg, compost) will actually begin to buffer the PH in both directions -- meaning it's really hard to move it away from a 7.0 (once fully degraded). Just a handful of tiger 90 will effect a dramatic change in pH on sand (which has a very low pH buffer capacity), but it's fairly ineffective on soil with a lot of organic material, as the organic material buffers the pH.