Decided to finally change the speakers in my '08 Fit. Looked around for tutorials and instructions, thankfully found details here and there. Here is a very, maybe even too detailed description of how to do it. if you have any questions, feel free to comment and ask. Will try to answer to the best of my ability.

The speakers I replaced the stock ones with were these polk audio DB651,

I also used a wiring harness off of crutchfield to prevent splicing wires.
Metra 72-7800 Speaker Wiring Harness For select 1991-up Honda and Acura vehicles at Crutchfield.com

link to step by step instructions:
Speaker Replacement - Album on Imgur

 

Nice photos/ write up. Thanks for that. Been contemplating changing the stock speakers, but after the suspension and minor repairs to the car I will have to wait.

 

probably the best $120 i invested in a while. and glad you found the pictures useful

 

Is it enough just to swap out the speakers for better audio? I may have to do this if so

I ask because on my last car I had to replace the speakers due to one of them cracking, and the sound quality was the same as stock, despite getting supposedly better aftermarket equipment. My fit on the other hand sounds pretty grainy stock, if this were to mitigate that, then I'd like to do it.

 

In 2013 I swapped my speakers for better ones, ( alpine 4 ways, it's overkill but they were 50% off, and Are still good, stock speaker lack mid rang, those alpine helped for that), but it was not enough. Although I don't listen to my music super loud ( I'm not the"I want my whole neighbourhood to hear my stuff", kind of guy), in higher level the Stock radio was not able to "feed the speakers" enough juice, bass and mid were fading out. So I swap the radio too a month later, for a double decked sony ( pay 150 + tax for it on special, 7 band equalizer, Bluetooth,usb, pandora, satellite etc, only draw back is the lCD is harder and is smaller than the stock one). The speakers are a pain in the ass to change, My new speker were a little to big, you would need those round plastic ( half a inch) to elevate the speakers ( the stock speaker magnet is ridiculously small). Plus somehow, screwing the speakers directly into to car chassis grounded them, So I install the bracket, than use small screw those fixed the speaker to the bracket, so no metal touched the car. I have kept the stock tweaters and those work just fine for me. The honda's speakers wires have a proprietary plug on them, so I've cut them, BUT don't do that, crutchfield have adapters, ( I discover that after I did the job and bought the dashboard bracket that you need for another radio). They sells everything you need. I really should have documented my whole experience. I would probably have to open my door again this summer, I might take picture and posted them here.

 

If i were you i would just replace the speakers and the headunit all at once. I replaced my headunit first and noticed a significant change, but due to the stock speakers being the POS they are, i was limiting myself. headunit, speakers and all the harnesses should cost you $300 tops.