You Crazy Americans!!!!
Drop the Kenwood box, and step away.......Don't look back.
No offence to anyone who owns Kenwood gear, but Kenwood is, and always will be a discount brand. Kenwood has some decent head units, but that is as far as I'll go. The reason so many people have Kenwood gear is because of the price point, but if one is serious about a good sounding sub setup, it should be the last brand on your list. Once again, no offence.
I have been through a gazillion diffrent sub+amp combos in my past 3 cars. In my experiences, the following brands of 10" woofers have performed very well:
1) ***Eclipse - any 10" woofer.
2) **Rockford Fosgate - Power or Punch HX2 10"
3) *Kicker - Solo Baric 10" or Impulse 10"
Other good brands that I havent owned, but have heard:
1) JL Audio
2) Alpine
3) Infinity (I find them to be way too expensive for the performance)
Since you're not looking for high SPL, I would suggest two tens to be optimal for your car. Why two? Well, if you're not looking for high SPL, then you go for clarity. If you have two woofers in your car, then pair them with a two-channel amp, then you can run your subs in stereo. A sealed box would be best for this application (ported box will move too much air, and a bandpass is just out of the question). A sealed box will give you tight, clean bass. The other two kinds of boxes are ment for SPL.
In terms of an amp, for you application, somewhere around the 400 Watt RMS rating @4ohms should be good. If you can send 200watts to each speaker than you should be where you want to be. Make sure when you get your subs and amp that you keep it at 4ohms, meaning your subs should be 4ohm subs, and your amp's rating of 400watts RMS is measured at 4ohms, not at 2ohms like alot of them are. Pay carefull attention to this when you're out buying gear. If you were to run a 2ohm setup, you would be making much more sound, but 1) you said you weren't looking for a bass monster, and 2) a 2ohm setup is usually pretty powerfull, so you're looking at caps and other power boosting and saving tools which cost money. Look for a class "A" amp if you can, you have no use for a class "D".
For the amp, I have had great experiences with the following brands:
1) Rockford Fosgate
2) Phoenix Gold (XS 2500 is a great one, good price point)
3) JL Audio
4) Kicker
If you have any more questions, I have been in car audio for about ten years, doing custom installs for five, and have helped put together endless systems for people just like you. Post or PM me.
Also keep in mind that just like a modified car, an audio system needs to be properly tuned. Refer to my post in this article which discusses the EQ spectrum and proper use of Filters.
Filters and spectrums.
Cheers.