If you can't get your players involved in your game just for the joy of squashbuckling, I suggest you start them off on weaker grounds to make them FEEL for their roles.
Have the Rogue Trader be some poor ganger scum living on the edge in Calixias. Then have the Senchal, an old family servant, rush to find him amongst the underhive while a rival Rogue Trader seeks him too. Accompany the Senchal by any other players who could be explained as either mercenaries, family servants, or those who still hold loyalty to the dynasty.
Continuing would mean having the RT's gang be killed, him swearing vengeance, meeting up with the Senchal, getting the Admin to acknowledge the authenticity of the heir, escorting a crate full of debts to the Imperial Governor's palace, getting a busted systems ship refitted with warp capability, finding their transport in ill repair, killing a bunch of void hereteks to garner AdMech favor, receiving the repairs, and finally having the rival RT dynasty show up in their fully fitted cruiser only to have the RT escape into warp. From there on out they head for the Kronus Expanse because it's the only place they can make a quick profit without competing with major merchant houses. There are dangers though.
As you can guess this is the path I chose for my players and it has turned out great. They love their guys and nearly every session has them doing some awesome heroics. The game may be centered around profit but that doesn't mean the characters do.
My PCs are a Hiver RT, NB Senchal, and VB Void Master. Their ship the Silver Bullet as she was named by the RT is a sword class hull with the Adventurous and Temperamental Warp Drive. The complications represent the fact that the machine spirit is eager to explore the universe beyond it's home system and that her warp drive was crudely installed. She's pretty minimally fitted due to the relative poverty of her masters; their PF started at 10 but is now around 25.