From the web .pdf, the 8454 has a better display, wma, digital input and has 8v. (This is only a benefit if using multiple amps, right?)
Is the SQ is the same?
Am I missing anything else significant that $150 gets you?
While I don't need ipod control (ala alpine), I would like a passenger to be able to play songs from one, is this possible?
Well there is one big difference, Digital Time Alignment. Both of the units have it but only the 54 can be set manually. The other unit only gives you the choice of picking your vechile type and letting the computer do the rest. So if you put speakers in non factory locations then the time delay is really of no use. Of course I am looking at this from a Custom Installers point of view.
Has for your question about the Ipod. You could make good use the 2zone/control available on the 54, not sure if the other one has it. Run rca's from the auxilary inputs then to the back some where. Then on the users end, put on a rca to mini converter. This would allow the person in the back to have their mp3 music while the people up front listen to another source.