Installing Chinese Navi

[polizeifritz]

I am planning on installing a Chinese navi system into my 1999 ES300. This is the unit I plan on using: http://cgi.ebay.ca/ws/eBayISAPI.dll?ViewIt...em=120417673070 I just have a few concerns.

Since the es has a 195watt 7 speaker system, will this unit be able to put sound to all speakers as the listing states 4 x 60 watt. Will this unit be compatible with the current stock amp and will I need an AMP bypass wiring harness or a regular one? And will I be able to use this unit with my stock antenna to get a decent signal? Radio is key for me. Finally if I get this all wired up through the amp, will the sound quality be ok with minimal electrical interference?

Thanks