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As some of you may know I've been fiddling around with designing my own sci-fi universe from the ground up. I am currently working on outlining the atmospheres for several of the different worlds in question and ran into a bit of a snag. One of my species in particular I wanted to give a biochemistry with Sulfur acting as the electron donor in the the photosynthesis/respiration process instead of Oxygen. The problem is I can't seem to find much that details the processes involved for this kind of respiration (or photosynthesis). I would need this so that I could adjust atmospheric composition of gasses like H2S and SO2 and anything else that was relevant (similarly to what I do on "normal" planets where I adjust the O2 level).

If anyone knows what the cycle looks like or a website that would spell it out pretty clearly for me that would be wonderful.

I'll be the first to admit that I don't have the background necessary to answer your question as it is; I can tell you that sulfur is a reactive nonmetal, as oxygen is, but forms an octatomic molecule rather than a diatomic one as oxygen does. As it is a science fiction universe you can fudge that until it fits, of course. I'm sure you can find somewhere the metabolic cycle of sulfur-dependent monerans from the deep oceans, and simply scale them up to your fictional multicellular organisms. Knowing that there are sulfur-metabolic organisms even here on Earth, I wouldn't take too much issue as a reader, but here's the issue I would have: if you have atmospheric gasses like H₂S and SO₂ in any appreciable concentration, you will invariably find them to be short-lived and will rather end up with atmospheric concentrations of things like H₂SO₃ and H₂SO₄ (sulfurous and sulfuric acid,) and other nasty things. As a reader, I'd demand a pretty convincing explanation of how an organism stands up to that sort of atmosphere.

Check out Robert Freitas' book Xenology, specifically chapter 8 which deals with alien biochemistries. You might get better results from an ammonia based lifeform compared to sulfur.

Now the other fun might be where the creatures have smaller cells, meaning more connections possible in their brains, allowing their Sentience Quotient to be higher (humans are ~level 13 intelligence, so imagine trying to outthink a level 20 intelligence).