I'm taking a page from an old Dragon Magazine article on the Imperial Bureau of Internal Security (IBIS). I like the acronym better than IRIS, and I've made the agency a sub-section of the Scout Service. Basically, my PC's will have been recruited as troubleshooters and agents in the Solomani Rim, provided with a ship (the Venture-class Frontier Courier), and will juggle missions from the IBIS office on Dingir with maintaining their cover as free traders/mercs.
The main literary inspiration of the game is McMaster-Bujold's Vorkosigan series, though visually, the clothes/uniforms, ships and tech I see as being designed by the Space:1999 Year 2 team.
I decided to do the Solomani Rim region, as I'd picked up the AstroSynthesis program a couple of years ago at GenCon, and have used the local star data to recreate the sector in 3-d. The players can plot their courses on the computer, and though some of the systems have different names than they do in the OTU, the amateur astrnomers, physics geeks, and science nerds that populate my gaming table will appreciate the attention to detail.