ssmoked

i have an amp and sub hooked up to my factory head unit to my 96' ES. now i need to change the head unit. some of the stores (best buy), said i need to bypass the factory amp. others such as (circuit city) said i dont need to. i just dont want to get ripped off because i am perferring Best Buy to do the job. does anyone have experince or had their head unit changed at a store??

thanks in advance