Audio transplant
 

My Mazda6 is gone, replaced by the RX-8. Just like the 8, the 6 doesn't have a dash kit, so with the 6 I ran an Alpine HU in the glovebox, controlled by the steering wheel controls. Boston Z's in the front, powered by a four channel JL 300.4, Image Dynamics 12 Max sub, powered by JL 500.1.

I don't plan on replacing the HU in the 8, so I'm going with the stock base HU. I have all of the components from my 6, plus a "leftover" Boston 110 sub (10 inch in very small box). I decided to gift the Boston Z's to my son to use in his new Mazda3 which has a dash kit, and he'll use the Alpine HU.

It was clear to me when I had the Maz6 that there is no way the audio will reach it's highest limits with the stock HU. The Z's with the stock HU will only highlight flaws, so I won't use them.

So....I have given thought to putting in 6.5's or 6x8 in the front and 6x9's in the back, running off the 300.4. Any recommendations for speakers (I have 75 quality watts x 4) for the front and back? Should I skip the back speakers? I'll probably also use the smaller Boston sub , but if the four speakers have decent bass, I might pass up on the sub to save space and weight.

Don't skip the rear speakers. Replace them all.

I take you only have the base stereo (you said, "stock base HU"). That makes all audio work much easier in this car.
You can install either 6x8 components (Infinity 6800cs is a drop-in size), 6x8 coaxial or 6.5 component speakers in the doors, whichever you like. Pretty much all of them are going to give you much better sound, even with the stock head unit. Since you're planning to use a separate amp, decide what you like and go with that setup.
With no sub, you will likely not have too good bass. I'd say, you definitely will need a subwoofer if you want a good bottom fill. There are many ways to do that - a simple sealed 10" box with an appropriate amp in the trunk oughtta do the trick. You can go more fancy, but it will cost more money if you want to have some sort of a custom enclosure.

There is a lot of good info in this forum - the search function is your friend, just need to take the time to find the answers. :)

Tamas,

Could you explain why audio work is much easier with the non bose system? Thanks in advance.

I've pretty much decided to use the JL 500.1 amp and my 10 inch Boston sub (very small) but I'm still debating as to whether to use the back speakers at all. I may regret giving my $1,000.00 ( as in ONE THOUSAND DOLLARS) Boston Z's 6.5's to my son, but I know that a speaker that good will emphasis the flaws in the stock head unit. When I originally set up my Maz6 with the Z's, I used the stock head unit, and the muddy mids and shrill highs drove me nuts, forcing me to go the "Alpine in the glovebox" route.

I have never used the rear speakers in any of my car audio setups. Should I do it in the 8?

You need to replace those back speakers--I did never looked back. Going to add an 8in in the trunk--just to even the sound out.

Because you don't have to deal with the Bose's non-standard speaker impedances (door speakers are 0.5 Ohm, for instance). Or the three separate amps.
Of course if you decide to ditch all the Bose speakers and amps, and install an own amp plus replace all the speakers, then there is not that much difference between the two.
However, if your goal is to replace the speakers, that is much easier to do in the base setup.

If I were you and had a 10" sub plus amp laying around, I'd hook that up and see how well it does. It is worth to try that out before shelling out money for a new sub. Plus, you can then reuse the hookup for the new amp anyway if needed.

Really, the sound of the RX-8's stock head unit (if you use it with a good separate amp) is not that bad at all. I know I'll be able to live with it just fine... :)
Certainly, this might be different with you ;)

And I would definitely recommend to replace and use the rear speakers as well - getting decent 6x9 coaxial speakers is not too expensive and certainly will add to the experience IMO.
You may want to think about giving the expensive 6.5 components to your son - they would work fine as front speaker replacements :D

Hey, a promise is a promise. The young boy gets the Z's. Maybe some focals for me?

That's what I have in my car :)
Focal Polyglass 6.5 components in the door, and I just went with a lower-end Access 690 6x9s in the rear.
The difference is night and day. And it wasn't even too expensive (when buying online).

Focal's will always out do the Boston's...i'd install them and then wonder why you even thought about the Z's again...