Actually, (this could be total misinformation, just something I've heard) a "reference-level" audio system is a system that achieves totally flat frequency response. This means that if you sit there with a dB meter and do a sweep from 20hz-20khz, you will get readings all at the same dB level. Obviously this is near impossible, so readings withing +-1dB are acceptable.
When I used to read around on DIY car audio forums someone had mentioned this as a tip for EQing a car system.
Just my 2 cents. Please don't yell at me if I'm wrong

It does sort of make sense though, because when movie directors make movies, they use reference monitors, which have perfect color accuracy and such (they make DVDs to "EQ" your TV as close to these settings as possible, just like they make test tracks for audio systems).