Please help - do I need to rewire for replacement receiver

[AttyGirl]

I recently purchased a 2002 Boxster as my second "fun" car (yes, women can have a midlife crisis also - we just get them earlier. . . ). I want to replace the factory stereo and add Bluetooth and aux. I found an Alpine receiver. I also found some new door speakers as the current factory ones do not appear to be working (at least I don't think that they are - when I fade to back there is no sound). I don't know a lot about car stereo systems - but I went on Crutchfield and spoke with a guy to confirm what I wanted to purchase.

Here is the question - I am being told that I HAVE to bypass the factory amp because if I don't, the sound will be worse than it currently is with factory unit. In order to do this, I will need to rewire the entire car. Crutchfield told me that the two harness sets worked with a 2002 Boxster - the guy who is going to install is the one telling me that it won't work. He said that the problem is that the Alpine unit will amplify the sound, then the wires will de-amplify it, and once it passes through the factory amp, it will be re-amplified - and finally the sound will go to the speakers and be crappy. He told me that this is a Porsche issue (and one of the joys of ownership).

I am confused (to say the least). If it needs to be completely re-wired in order to sound good, I'll do it. It's just after browsing through info on the web, I'm not sure if I need to. The reviews on Crutchfield for the harnesses say nothing about reduced sound quality - and several of the posts are with respect to Porsche Boxsters.

Also, the guy at Crutchfield told me that I should spend money and replace the dash speakers - and the guy installing said that I should only replace the door speakers. Thoughts??

I'd really appreciate any information. Thanks!!