Hey dude,
So your Pioneer deck is a bit dated.....this could be a bit of a problem. Yes, you could run your subs off of your current setup by splicing your rear speaker wires and attach a line-level converter (changes a straight wire to an RCA) but this never ever turns out well. My advice would be to get a new deck that has designated sub preouts. You can get them pretty cheap nowdays. If you have the choice, get a deck that has high-pass and low-pass filters as well...best money you'll ever spend.
Get the proper wiring harness as well...cuts your install time in half and they only cost like $15.
Good luck on the install, and post or PM me if you have any more questions along the way.
Here is a bit about filters from an old post and why they are so usefull.
Cheers.
your midrange speakers are one small part of the puzzle here . The MAIN part of getting a good sounding mid and high range of audio is your head unit. I'm guessing you are running the speakers off of your deck since you didn't mention an amp of any sort. Having access to filters through your head unit is the only way you will achieve desirable results when looking for crystal clean audio. Utilizing a High pass filter (assignable to cut out low distorting frequencies), and a low pass filter (assignable to cut out distorting high frequencies), you will be able to fine tune your speakers to the acoustical properties of your car. Ever notice that when you install speakers, throw in a CD and crank it up, it sounds like crap? And the higher you turn it up the more you have to start turning down your artificial EQ parameters (Bass+Trebel controls) to get rid of distortion? That's because your midrange speakers are not designed to handle sub bass frequencies (30-100Hz). That's the job of a subwoofer. And if you are not using filters of your head unit, you are sending your midrange speakers these distorting frequencies and creating un-necessary cone movement in your speaker. What I mean by un-necessary is that a speaker, just like any other sound emmiting device, has to abide by the laws of the EQ spectrum. A great recording will have each instrument "carved" out onto a specific place in the EQ spectrum, so that when it is played through a device (speaker) no two instruments will be fighting for the same frequencies, therefore cancelling eachother out and creating noise (distortion). If you have a speaker that is taking on too much sub bass frequency and creating unnecessary cone movement, then the rest of the low end frequencies will suffer because they cannot move the cone properly to create the proper sound. Hence using a filter. If you can keep your gains (volume) at it's maximum potential, and cut out the low distoring frequencies, then you can optimize your speakers and have them sounding crystal clear and loud, without any distortion, and also a lessen the load that will extend the life of your speakers as well. You can use this same process to "carve out" a spot in the EQ spectrum for a subwoofer if you ever decide to get one by cutting out useless high frequencies.
If you dont know what I mean by the "EQ Spectrum" think of it this way: A normal EQ goes from left to right, or Bass through Trebel (Bass.......Middle..........Trebel). Take a normal band for instance. Each instrument will fit into one of these three areas. A bass guitar will play low frequencies, lead and rythem guitars will play in the midrange, drums will play all over the place (Kick drum in Sub Bass, snare in midrange and hats and cymbals in high range). As I said before, a good recording will have carved out a specific spot in the spectrum, so that no two sounds are "fighting" for the same frequency on the speaker, becuase when the two conflict, then you get distortion or cancellation fo both sounds. Same goes for listening to your music.
Ryan.