Tom, I use the internal cross-over in the head-unit as well as the on-board cross-over on the amp to control the frequency that the 4", 5 1/4" and 6.5" speakers get. That's the beauty of the Pioneer head units. They have speaker and subwoofer controls in the audio menu. I can turn the subs on or off, control their frequency and level and the internal cross-over allows me to determine the amount of lows that go into the small speakers. In your case, I would get a small 8" amplified bass tube for your Z. You run a small power wire to it then ground the unit as well. Then run a set of RCA's or speaker wires to it (from the head or directly from the speakers) for signal. This will give the system that "Low end" that it needs and that you've been trying to reproduce with your 4" speakers.Then you can install some non polarized capacitors (about 4.7 Uf or 47? can't really remember) onto the 4" speakers (+) wires and this will eliminate the lows from them. The bass tube has an internal cross over that will block out the hi's. The bass tubes usually have a "Quick disconnect" plug which will allow you to easily remove the tube when needed. So basically, the 4" speakers are for the hi's and the tube is for the lows. You can't rely on 4" or ANY small speaker to reproduce the low ends needed for a decent sounding system. As for your first question, on the roof..... Kinda like a San Francisco police car, "Pull Overrrrrr" I'll be doing a full picture type write-up on the install on the 260Z when I get to that point. As I've never done a 260Z stereo system, it should prove interesting and educational all at the same time. I'll be running new signal and speaker wires from the head unit to the rear in line with the OEM wiring. I'll also be running new antenna control wires, hatch pop wires, hatch pin (alarm) wires and anything else I think of between now and then. Dave. By the way, the less low end that the 4" speakers are trying to reproduce, the louder they will go without distorting.