I also have an 04 GX - I bought a 9" clarion and had it installed by a local shop. It has a FM mod so you have to tune your radio to a certain frequency to get the sound from the speaker system. The clarion comes with two sets of wireless headphones which are really good. The picture is one of the best in business. My advice would be to go with a good name brand. Saving a few buck on this is not worth it. My installation cost about $150 and the tech did an excellent job he got the power wired straight from the battery with additional fuses etc. Really clean job and would recommend him if you are in the DC metro area.
Thanks for the reco, unfortunately, I'm in socal...Do you know where he ran the wire, esp. in lieu of the moonroof, as well as the side curtain airbags? Also, any other suggestions to tap the wiring as opposed to the battery up in the engine bay? I'm assuming might be easier to grab behind the existing radio harness/panel when the in-line modulator is installed???