So I'm still kicking around ideas on this upgrade and was wondering how much room we have under the passenger seat? Would something like this sub fit underneath there:

Rockford Fosgate PS-8 Punch Series powered 8" subwoofer at Crutchfield.com

Thinking this might be a cool and easy to install solution that wouldn't take up any space to run with the HU??

Pretty tight under the seat. What about behind one of the seats? Or it's small so maybe mount it in the hatch area. Would it fit inside the spare tire?

Yeah perhaps inside the spare would be an option, but would loose the spare. That would be the only other option really. It's only about 3.5" tall...

Sorry when I said spare I meant inside the rim itself. I have the sport with the bose system. The subwoofer is located inside the rim. I thought if your rim was open you could mount it to the removable panel under the mat or inside the rim somehow. From your previous posts I read you want to install components without a amp. I have done this before with a new head unit and they sound much better then OEM. True you won't get much bass punch but they are not built for that. Just try to match the stereo RMS with the speakers RMS to get the best output from them. It wouldn't make a difference at this power level to upgrade the speaker wire. You can get a kit to bypass the amp and use factory wires.

The Kenwood Ksc-sw11 is even smaller.

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So, I'm still kicking around what to do with my audio upgrade. I know I am getting the 4100NEX for my headunit.

But with everyone saying it's not worth upgrading speakers without adding an amp -- I am now seriously considering adding an amp. The wiring doesn't seem all that difficult. I would just want to put it under the front seat.

Would it be ok to add something like the Polk DB6501 to the NEX without an amp, and just get a mono block amp to add a small sub in a zenclosure??

As that this is the route I am thinking of going??

Thanks so much for all your help and thoughts...

I changed out my door speakers, and while I'm sure I'd get more out of them with an amp, they still sound way better than the stock speakers just powered off my Kenwood HU.

I am considering adding a small powered sub like the Kenwood ksc-sw11 or kicker hideaway. Which would have their own amp. I think one of them would work great behind the passenger seat.

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Tarheel -- thanks so much. Yeah, I'm thinking I'm gonna stick with upgrading the speakers while I have the car torn apart (again -- already did it once to sound deaden the whole care).

I was looking at those same hideaway subwoofers as well. It's that behind/under the passenger seat. Or I was going to get a simple rockford punch mono block 250watts and do an 8" driver in a zenclosure...

Still have not pulled the trigger on anything and have a question about these Focal PS165V component speakers. They are plenty efficient at 92.5db.

Interesting this about these is they have SEPARATE crossovers for the woofers and tweeters.

Being that the 370Z cabin is so small with only front components -- would it be possible to run these off a 4100NEX using the front output for the woofers, and the rear output for the tweeters? Then just run the auto setup/EQ on 4100NEX to tune everything??

This would then be a 'semi-active' running off the head unit??