I recently took my 12 inch Rockford P3 and 500 watt Alpine MRP-M500 out of my SC300 and put it in the LS. It sounds alright and the headlights don't dim even when I turn it up loud. It's a wimpy setup though.
I plan on getting a 13" JL W7, Rockford T1500, Rockford T400 and some speakers in the next few months though. Where did you find that high output alternator? I didn't know they made one.
93 Lexus SC300
02 Lexus LS430
05 Lexus LS430 UL
95 Toyota Supra