sorry tony, yeah, I'm the guy with the M-audio Firewire Solo and a mini and I've had DTS pass-through since day one with Apple dvd player, all the way from 10.3.8 through 10.4.2, but the Solo is a newer product than the Audiophile, I'm not sure if that's made a difference.
What driver are you using--1.5.3?
Besides checking in DVD Player audio preferences to select the M-audio device out, have you also looked in Utilities > Audio MIDI Setup and also in System Preferences > Sound > Output--you should see it there as well. Select the Audiophile in all three and try your DTS again.
I took a look at your model's software control panel online and it is a little more complex than mine--and I'm not at home so I can't verify exactly which boxes in which menus are checked--but from what I remember, in that first mixer column "1/2 sw rtn" I have both the "1/2" button and the "spd" button highlighted--so when I switch between iTunes and surround passthrough with Apple dvd player, I never have to change any setting within the Solo control panel--it just works. It'll be another day before I'm back in town and can check settings on the Solo itself. Under the "output" panel do you see a choice between "pass through" and "mixer?" Have you tried both?
If none of this works, the other thing I noticed on the M-audio site is that under the Solo it says "OS X 10.3.5 or later required for Dolby Digital and DTS pass-through with Apple DVD player" while under the Audiophile it says "OS 10.3 required for Dolby Digital and DTS pass-through with Apple DVD Player." I'd call up tech support and ask can it be that the "or later" was not inadvertantly left out with the Audiophile?