Shawn350

Hey everyone! I just got a 2014 GS350 base a few months ago, and I love it. Except the audio. I came from a 2006 Miata that had a Bose system, and it sounded way better than the base gs350 system. So anyway, I read over the forums and did what a lot of people said, get a sub, and then see if you still need new speakers. I got 2 10" phoenix gold subs, and it really made a differences when its at lower volumes. But when I turn it up, I still feel like its missing something, its just kind of flat. So I've decided to upgrade the speakers as well. I was wondering what is the best way to upgrade the dash speakers. The installer said I could save some money by not replacing the one center dash. Im willing to spend the money if it would make a difference. I also got an idea of having him replace the stock rear deck sub with a 6.5 regular speaker to have more of an immersive listening experience. I don't know much about audio, so I don't know if that's a good idea or not? Thanks for any advice you can give!
Here are a few pictures of my sub.

tejanp

I have been out of the audio game in quite a few years but is that the best placement for a sub? against the back seat and not ported?

Shawn350