What stereo upgrade next?

one other question what is the difference between running a sub at 4 ohm vs. 2 ohm.  Which is more power 150 watt rms @ 4 ohm or 150 watt rms @ 2 ohm?

I don't think there's much difference in those amps, they're all comparable.  I also wouldn't trust any of them to run 2ohm in bridged mode - roughly the same as 1 ohm stereo.  150 watts = 150 watts at any ohm level, question is can the amp do that?  any of those should be OK at 4ohm bridged.

so is there any benefit to running the sub at 2 ohm vs 4 ohm?

If I were looking at enclosed sub boxes and contimplating building my own, is there any difference in a closed box?  I have seen some for $25.  Is there anything I should be looking for?

What do you mean by "enclosed" and "closed" box? Are you talking about a bandpass box? A sealed box, ported box? Any how, If you are good with woodworking then build your own. Big Dave

Sealed.  I was just wondering if a sealed box is a sealed box or what makes one better than another?

Well ones not any better than the other, it's what "you" want. Some people like band pass, some like ported, some like sealed. I use sealed my self I think they sound better. ported and bandpass are more for spl. this web site has all the info you need read all it has to say. Big Dave

I spent some time reading the sub section yesterday and I'm on information overload.  I have a 2002 liberty and want to add some bass to my system.  I don't want window shattering or car shaking.  Just want to help my alpine components out for better overall sound quality.  I'm assuming adding the sub will give me a tad more head room on the front components since they will not have to reproducte the bass.  I just want to make sure that whatever I buy will do that.  Don't want to buy too much or too little.  Contemplating a powered sub or building my own.  I have read some good things about bazooka's and some bad things.  Same with audiobahn.  I was leaning twoards a tube since size is an issue with the small cargo area.  Any suggestions?

I would use a single 12. and say a 250wrms amp. build a seald wedge box. Seeing that you already have alpine speakers I'd get an Alpine amp and sub to.   Go to your local shop and see what they have or Best Buy they carry Alpine. I think you would hit pretty good if you wanted too, or you could tone it down if you don't feel like hittin hard.Big Dave