bass tube or sub box for my old bmw?

I currently have a pioneer xm head unit and 4 infinity reference speakers. I want to add an amp and a sub. Do you have a suggestion for a fairly priced amp and sub. I am not looking to spend a lot. I guess it would be a single subwoofer or bass tube and an amp. Thanks

Any idea on how much not a lot is?? I am guessing you have the speakers powered off the head unit. What are your thoughts on building a subwoofer box and wiring up the amplifier?

Maybe a setup with something like this
http://www.onlinecarstereo.com/CarAudio/ProductDetail.aspx?ProductID=18053

and
http://www.onlinecarstereo.com/CarAudio/ProductDetail.aspx?ProductID=19666

add another $30 for an amp kit, and another $30 for materials to build a box.

Mainly recommending the Infinity cause you already got infinity speakers, and I had a pair of the older version of that sub and I thought they were a solid performer.

Maybe jumping up to a 5 channel amp with a single 12" or 10" sub would really wake up the sound. Guess it all depends on how much you want to spend and how much bass you are looking for.

I was thinking of that sub, but maybe even just going with the 10 inch. Could you suggest a box that is already made that the speaker could just drop in to? What about one amp that would run the 4 speakers and the one sub? I was kind of hoping to spend 400 or less. But not sure if this is possible.

For 5 channel amps there are a few options but many start to get pretty expensive. Here are a few that shouldn't break your budget.

Infinity 5 channel
http://www.onlinecarstereo.com/CarAudio/ProductDetail.aspx?ProductID=19427

Hifonics 5 channel
http://www.onlinecarstereo.com/CarAudio/ProductDetail.aspx?ProductID=16362

Then for subs and sub boxes you can just match the recommended volume of the sub to the internal volume of the box. Not sure where you plan on buying all this stuff but I know Circuit City, Best Buy and any custom audio shop will have boxes and such. They can also be found online, and I think ebay even has a bunch on there.

Going with your 10" Infinity http://www.onlinecarstereo.com/CarAudio/ProductDetail.aspx?ProductID=18599
A box like this would work, http://www.woofersetc.com/index.cfm?fuseaction=product.display&Product_ID=3521
It's a little big but that shouldn't hurt you any, the sub itself will also displace a small amount of volume, but not much maybe something like 0.09ft^3 or so.

Then for the 12" Infinity http://www.onlinecarstereo.com/CarAudio/ProductDetail.aspx?ProductID=18536
A Box like this would work, http://www.woofersetc.com/index.cfm?fuseaction=product.display&Product_ID=3520
Its small by the recommended volume but only by 0.05ft^3 and again shouldn't affect the sound of the sub too much.

Looking at about $408 if you were to get the Infinity 12" sub, the Hifonics 5 channel, the 12" box and I added in $30 for an amp kit, 4 gauge kit would work.

Thanks man, I appreciate your help. It is now time to start shopping. Thanks

no problamo, glad I could be of assistance.