USAspec just released their ipod adapter for the newer Hondas/Acuras (Includes 04-06TLs).
http://www.discountcarstereo.com/detail.aspx?ID=879
For NAVI & XM compatible, they recommend a Y cable that allows you to tap into the BUS. I believe this is the same way the music link adapter works. Unfortunately, this adapter does not display text. Maybe they are only able to read the commands on the bus, and don't have the propers chips/timing to write to the bus? Hopefully, you can figure out how to do both.
Anyway, hope this helps with your project. I'm still interested in beta testing with my 05 TL navi.