I noticed the game was crashing on launch, so I poked and prodded it and got it to work. Here's what I did (I'll keep it simple for those who aren't technical masters).
1) Install it through Crossover
2) Download d3dx9_36.dll from http://www.dll-files.com/dllindex/dll-files.shtml?d3dx9_36
3) Put the d3dx9_36.dll file into "/Users/*your username*/Library/Application Support/Crossover Games/bottles/*name of the wine bottle you installed SINS into*/drive_c/windows/system32" (you can cut this trip in half by going into Configure > Manage Bottles > *wine bottle you installed SINS into* > Advanced > Open C: Drive in Finder). Go ahead and say "replace" to the dialogue window that comes up.
4) Go to Configure > Manage Bottles, then click on the bottle you installed Sins into and click Control Panel, then launch winecfg
5) Click on the Libraries tab, input "d3dx9_36.dll" (without the quotes of course) under "New override for library," click Add. This will add this .dll file to the bottom of the list. Scroll down and click on it in the list, then click on "Edit." Click "Native (Windows)" and press OK. Then click Apply at the bottom of the page, but don't exit yet.
6) Click on the Graphics tab and uncheck these two options: "Allow DirectX apps to stop the mouse leaving their window" and "Allow the window manager to control the windows." Click Apply, then OK.
7) Now click Programs > Run Command.
8) Under "Use Bottle," make sure the correct bottle is selected. Under Command, click Browse. Navigate to your SINS directory (usually "Program Files/Stardock Games/Sins of a Solar Empire") then click on the "Sins of a Solar Empire.exe" file and click OK.
9) Back in your Run Command window, click "Save Command to Programs Menu" and click run.
There are only a few extra things to note...
One might notice that all the fonts are extra big. You can fix this problem (for the most part) by downloading www.honorguardonline.com/sins/sinsfontfix.tar.gz, unpacking it, and moving all of the font files to *SINS directory*/Fonts. Make sure you replace all files.
Also, the video tab in the game (under options) appears to be blank. But you can change these settings by navigating to "*C Drive*/windows/profiles/crossover/Local Settings/Application Data/Ironclad Games/Sins of a Solar Empire/Setting" and opening user.setting with TextEdit. Here you can change the resolution (for both fullscreen and windowed settings) and play with the texture quality. You might have to input something under "PlayerName" at the top to get any settings to stick, but I'm not sure.
Also, there seems to be a slight problem with the game crashing sometimes. Usually this happens to me if I've been playing for a long time, or if I create and play a gigantic map (I tried one with about 1000 planets and many stars). After looking at Crossover's log files from these crashes, I'm seeing this error:
 wineloader(2478,0xa02d8720) malloc: *** mmap(size=2097152)
failed (error code=12)
 *** set a breakpoint in malloc_error_break to debug
Not sure what to make of this.