The Kindle DX pdf support does not support changing font sizes, nor zooming or panning. I gather that Savory does all these for the Kindle 2. Is my inference correct? Have you any plans for Savory on the DX?
I'm finding that math is rendered well on the DX, but even in landscape mode (where larger fonts are usually used) it can be a challenge to read. Worse, in landscape the (half) page breaks are 'hard' so you cannot choose to display a particular part of the page--if what you want falls on different sides of the break, you're out of luck.