Well if you want to work the extension on your theme, not on sitesplat theme, its a custom work(ask the developer). Or you have to do it your own. I'm not a coder myself (at all), but do you know if the code is open source? I'd assume not since it's hidden behind paywalls. Its time! Never too late....
Too bad that sitesplat extension is meant for digital downloads and not physical products though. Too bad you are forced to buy a theme to use it. sigh. Physical marketplace of sitesplat are so ready to release :D I only trust professional awesome coders with great theme. I first discovered the The...
You can try to register if you want to see my working phpBB marketplace www.phildiscuss.com,
Captcha: "digong"
See the link(Downloads) under the ADDONS menu, pm me for more info.