Brian,
(sorry for jumping back into the thread, but I did want to share....)
I don't believe you'll be able to use your FM system. I'm gonna take a stab at this, and hope that someone corrects me if I'm wrong. We also use Phonak's system...well, we would if it worked well for us, but that's another story!
Your daughter's boots are receivers, and require an FM signal to be transmitted to them. Disney doesn't broadcast an FM signal that her boots will receive. You'd have to take your transmitter and hook it directly into whatever sound system Disney is using....just like you do at home...you hook the transmitter into your stereo and it transmits FM signals to your daughter's receivers.
The ALDs that Disney provides are also receivers, for the signal that Disney does provide...either infrared or maybe induction (I can't remember for sure.) I don't think they will transmit an FM signal, so hooking your transmitter into them won't get you an FM signal to transmit to your daughter. (OK...I'm rereading this, and now I'm thinking, "Why not?" It's just sound, right? Hmmm...) The plugs you see are most likely either for physical headsets or for telecoil loops. I'm pretty sure the only way for the Disney ALDs to get sound to your daughter is either with a physical headset over her ears or with a loop around her neck, transmitting to her hearing aid's telecoil.
Your best bet is to try to use the telecoil in your daughter's aids, if she has one, but our experience, as noted above, was very poor with all the different ALDs that Disney had to offer. I tried, like you, to make arrangements ahead of time, unsuccessfully.
I hate being a "complainer", (I mean, really, it's Disney...who in their right mind can complain???) but I wish I had known ahead of time how unlikely it was that we would have success, based both on our experiences and the responses from the Guest Services CMs. I think I wouldn't have been nearly so frustrated, nor would I have wasted so much time trying to get a working set-up.
For adults who can read and those who can sign, it seems that services are at least adequate and most likely better than that. For pre- and early-reading children who use hearing aids and who do not sign fluently, access to speech and story lines can be very limited.
If you do plan on using their devices, be sure to take a stethoset or some type of testing device so you can hear for yourself what is happening. Had I used their devices without checking it out myself, my daughter would've been listening to nothing but telecoil buzz!
The other thing I would suggest is working with your audiologist or Phonak directly to ask if a public infrared receiver with a plug can send a signal to your FM transmitter to be received by your daughter's boots. I am certainly no expert, and have failed miserably at all attempts to use anything beyond my daughter's hearing aids! Verifying with Phonak themselves is the best thing you can do ahead of time.
Good luck, and be sure to come back with a report. As more and more hearing impaired children are identified at an earlier age, it will be interesting to see if changes are made in services available for them at the Happiest Place on Earth!
Amy