If you want a subwoofer, simply get those that fits the budget. If you want a proven and affordable choice, get the JBL GT5 (2.5k~ish) that's even being used for home audio purposes. Xmax is a parameter that measures one-way linearity and theoretically, gives you an idea of the subwoofer's SPL capability. However, this isn't the case in real-world applications since some manufacturers overstate their Xmax parameters (hint!) and you have other factors to look for (ex. motor, basket type, power handling, box size, etc.). As a practical example, if you put a 12" CV Stroker with 20mm Xmax against a 12" JLW7 with 29mm Xmax, the CV would still win in a loudness match even though its Xmax is lower.
*Brennt
For 5k, you have the alot of choices on your sleeves: Morel Maximo, Firlands EV602/612, Domination D'Lites, Ryan Audio, etc. Don't ask which is the "better" one since there's no such thing as "better". It really depends on your choice. I would suggest asking for the best deals in town, getting the best one, then use the remainder for deadening your front doors. If you'll ever won't be putting an amplifier, find the one that has the highest sensitivity rating (ex. 90dB > 85dB). This way, you do not need a boatload of power to drive the speaker to your desired volume. If you're willing to stretch the budget by 1k, get the Cadence ZRS6K.
Last edited by jhnkvn; April 6th, 2012 at 08:49 PM.