Several options. Which one is best depends on your budget and system goals. Short term cheap, fix the amp again. Shop might make you a deal since they did the work once and declared it bullet-proof. Worth a shot.
A more upgrade option, if the speaker itself is okay, get something like the Dayton SA1000 to power it. For $400 you will have more power and lots of flexibility with adjustable phase and level, and even a parametric equalizer (one band, but still...) and the big advantage with this option is it sets you up for....
The best long term solution for really good low bass is a distributed bass array of 4 subs. The beauty of this is you start with the Klipsch sub and Dayton amp, then upgrade by adding additional subs. The low quality of the Klipsch will matter less and less as you add subs. Improvements each step of the way will be obvious, and if you get to four you will be amazed to find you have the best bass you ever heard, including systems much bigger/more expensive.
A more upgrade option, if the speaker itself is okay, get something like the Dayton SA1000 to power it. For $400 you will have more power and lots of flexibility with adjustable phase and level, and even a parametric equalizer (one band, but still...) and the big advantage with this option is it sets you up for....
The best long term solution for really good low bass is a distributed bass array of 4 subs. The beauty of this is you start with the Klipsch sub and Dayton amp, then upgrade by adding additional subs. The low quality of the Klipsch will matter less and less as you add subs. Improvements each step of the way will be obvious, and if you get to four you will be amazed to find you have the best bass you ever heard, including systems much bigger/more expensive.