sub suggestion

I would run a separate wire for the amp, and 10 gauge is too small no matter what anybody says.  10 is cool for the head unit, but not for an amp.  Go to 8 gauge or better.  I use 8 because I know that my system is going to stay at a limited power, and I'm running it at a high ohm load.  But it's not worth it to run that 10 ga. wire to the amp and then find that you have to replace it sooner than later.

“Im not sure if i want a bass frequency or anything below 50-70 hz in the back” … I assume you mean the Kappa’s and not the sub.  Well your going to be crossing the front and rear speakers over if you want to get clarity and volume out of them.  What kind of deck do you have?  Does it have crossovers for the amp?  I assume you have 2 pairs of preamps on the deck and will be running the front and sub off a different set.  Use the crossovers on the amp with the ones on the deck.  For instance my suburban runs a Kenwood 6.5” component set in the front and JL 5.25” in the rear with a JL 10w3 subwoofer.  All ran off of a Jensen 4 x75 amp with channels 3 & 4 bridged to 200w (even though it does not advertise as 2 ohm stable bridged, it apparently is because the voice coils on my sub are in parallel, so I don’t really know how much is going to the sub, but its more then 200w).  I use the deck on the 5.25’s, crossed over with the deck at 120hz (I fade them out to).  The Amp has the crossovers turned on, the front are high pass at 80hz and the sub at 100hz low pass.  But I also have crossovers on the deck, that I use in addition.  That way I can shape the sound according to the music I am listening to. So, if you have a deck with Xovers you can really filter out the low bass, so instead of cranking the xover up to 180hz to keep the 4” from popping, you could cross it over twice at say 120 or so, giving you a fuller sound up front.  Ideally you want larger speakers up front, but you could sound nice if you have quality 4” speakers up front.  The 4” will have its limits, but your setup will be crucial to good sound.

I second what Stevdart said about the gauge of your power cable.  I think at this point 10 is fine though, but if you do anything else your going to want bigger, say 8 gauge.  If you have not ran your wire, do it with 8 gauge, you’ll only spend a few dollars more then 10 and you’ll be ready for future expansions.

You should browse www.sounddomain.com for ideas on your system, here are a few:  http://www.cardomain.com/memberpage/201380/1   http://www.cardomain.com/memberpage/271887/2

1.“Im not sure if i want a bass frequency or anything below 50-70 hz in the back” … I assume you mean the Kappa’s and not the sub.  Well your going to be crossing the front and rear speakers over if you want to get clarity and volume out of them.  What kind of deck do you have?  Does it have crossovers for the amp?  I assume you have 2 pairs of preamps on the deck and will be running the front and sub off a different set.  Use the crossovers on the amp with the ones on the deck.  For instance my suburban runs a Kenwood 6.5” component set in the front and JL 5.25” in the rear with a JL 10w3 subwoofer.  All ran off of a Jensen 4 x75 amp with channels 3 & 4 bridged to 200w (even though it does not advertise as 2 ohm stable bridged, it apparently is because the voice coils on my sub are in parallel, so I don’t really know how much is going to the sub, but its more then 200w.  I use the deck on the 5.25’s, crossed over with the deck at 120hz (I fade them out to). The Amp has the crossovers turned on, the front are high pass at 80hz and the sub at 100hz low pass.  But I also have crossovers on the deck, that I use in addition.  That way I can shape the sound according to the music I am listening to. So, if you have a deck with Xovers you can really filter out the low bass, so instead of cranking the xover up to 180hz to keep the 4” from popping, you could cross it over twice at say 120 or so, giving you a fuller sound up front.  Ideally you want larger speakers up front, but you could sound nice if you have quality 4” speakers up front.  The 4” will have its limits, but your setup will be crucial to good sound.  2.  I second what Stevdart said about the gauge of your power cable.  I think at this point 10 is fine though, but if you do anything else your going to want bigger, say 8 gauge.  If you have not ran your wire, do it with 8 gauge, you’ll only spend a few dollars more then 10 and you’ll be ready for future expansions.  3. You should browse www.cardomain.com  for ideas on your system, here are a few:  http://www.cardomain.com/memberpage/201380/1 and www..cardomain.com/memberpage/271887/2  

I would go sealed, a little SPL can be gained by going ported, but ported boxes provide little room for error to get good sound.  http://www.jlaudio.com/subwoofers/pdfs/10_12_15W0_MAN.pdf  Have you thought about building your own box?  Its not so hard if you have the tools and alittle experience.  Glue, screws, wood and mounting/connections for about 30$.  You can paint it black for cheap or carpet it for 10-15 dollars more, carpeting can be more tricky then building the box though.