I'm looking for help identifying a particular young-adult sci-fi novel I remember reading while in high school, more than a decade ago. I still remember the outline of the plot quite clearly, but my searches haven't turned up anything.
The novel takes place in a future where humanity is suffering from 'ennui'. There are FTL-capable spacecraft, but the FTL engines to those spacecraft are provided and maintained by a friendly alien race. Members of this race serve aboard human ships in isolation, maintaining the engines. Humans are not allowed to be present or to observe the installation or removal of these engines.
The main character is a university student whose university (which is aboard a spaceship) crash-lands on some planet. I don't remember most of what they did aboard the planet, but they eventually discover that:
The engines are actually some sort of massive sentient living creature that feeds on the 'life-force' (or equivalent) of other sapient races (hence the 'ennui'). The 'friendly' aliens are the previous victims (and present-day slaves) of the antagonist race. The novel ends with a battle between some human ships with a prototype human-designed FTL drive and some of these beings.
Other odds and ends include 'Auditors' belonging to some powerful religious organization and robots referred to as 'deadmen'.
I don't remember the novel being particularly good, but the conceit stuck with me, for some reason. Any help identifying would be appreciated.