Does anyone here have an opinion on this (Bavarian Autosport / Infinity Basslink "Plug 'n' Play" Subwoofer Kit) upgrade? It's on sale for $349.95.

I am looking on upgrading my bass and this kit seems to be the easiest way to do it without spending big money on. What do you guys think?BTW, my '06 X5 has the DSP premium sound. Any advice would be greatly appreciated!

Thanks!