Joes GS300

Ok I have looked a bit but I am hoping that some smarter people than myself might be able to help me out. First I have a low mileage 2004 GS300 with the stock base stereo with a sub. I am a bit spoiled when it comes to my tunes and I am not sure I will be happy with the base radio. I have an Ecplise 5435 Navigation system from a few years ago that I can pop in for free (well free minus parts) 1. Does anyone know what wire harness I would need? Best Buy was trying to tell me that I needed a $150 adapter because it had a sub. Is this right? 2. What size sub is in the rear deck? Can it be replaced with an after market with a seperate amp? 3. Did I read right that the door speakers are 4"? 4. Is there anything else I should know? Thanks a ton everyone

Thank you, I am learning alot here. Hopefully I will get some great info on my problems

Ok first off brand new here. I bought a 2004 GS300 last week with 55K and not driven a day in the snow. It is a great car and I love it. There are two problems that I have found. One is the front headlight. The small black tab that secures the headlight snapped on the driver side headlight. This has caused the headlight to sink back a bit. Long story short I need to replace the headlight, being the age of the lights I probably need to replace both. They are not HID lights, I was hoping to get an upgrade to the lights, what are the best options? I have heard that the aftermarket ones on Ebay are crap, are there any that are decent. My old car had the Xenon lights and I loved them, these seem very dull after driving the old car. Also I am getting a small drive line vibration above 70 mph, it comes and goes. (it is like a shimmy in the steering wheel) All the tires have been balanced and rotated. Because it comes and goes I wouldnt think it would be a rear drive shaft out of balance, or alignment, but I am not sure. Any ideas? Thanks Joe