Hey man. I am right now in the prosess of building a stealth speaker-grow. I have done a speaker grow once before aswell... I´ll have somewhat more space than you to play with, but i have learned alot about growing in very small spaces .
Firstly, how big is the cabinet? Is it one of those big ones, or a normal one?
Is this a stealth grow? And if it is, how will you deal with the smell?
I guess fan noise is not a problem, seing as this is a PC.
100+ watts in that small a space will produce quite alot of heat. I had a 60w cfl in my speaker and and heat really was a big problem. So big infact, that I could not get the temps under 35 Celsius, even with fans. And this severely hindered the growth and lowered the quality of the buds.The main problem for this was the carbon scrubber. But your space is even smaller and with almost twice the wattage. On top of this the bulb will get very hot. I burned the entire top half of my plant because the bulb fell down on in. It will fuck up all plant material in the near vicinity. I learned this the hard way. Think of how sad this situation was for me. Just a couple of weeks to harvest, and all my buds go up in smoke, without me being present... Horrible lesson.
The "safety-distance" the plants have to keep away from the bulb, is pretty space consuming. In order to deal with the heat once and for all, I would deffinatly get a cooltube. I just built my own last week for about 50 bucks using a vase. Attach a fan inline to this cooltube, and the heat problem should be solved. I cant guarantee that the plant can rest against the cooltube, but it should be close. That would depend on the fan and thickness of glass perhaps. The cooltube will free up alot of space inside the PC, allowing for a bigger plant taking advantage of getting closer to the light. You know, the inverse-square law and all.
Then you need to get some ventilation going. Here you could consider a carbon scrubber, if smell is an issiu.
Ive seen some posts around the web where dudes with sick training skills can tame a plant like a bonzai, making it look like a work of art. Some almost seem to have nothing but buds growing from the pot. I have no experience in doing any training, and not much either in strains. My best guess would be an autoflower of some sort. If these are small-strain autoflower, maby you could even have two of them. But again, i dont know much about strains and such, so I dare not say more.