Here's a quick guess: What ouput are you using? There's the SW/LFE output on the back and also a preamp sub output. I would think you should be using the SW/LFE output.
I just looked at the KLH home page. It looks like most of their powered subs feature speaker level and line level inputs. Make sure you are using the line level inputs on the sub. Don't use the speaker level and also avoid the LFE input. This will allow the sub to receive the full signal from your 1050.
You may also want to try a crossover point that's at 100Hz or lower. I would believe your speakers should be able to go that low on their own.
Keep your front speakers set to "Small" to enable your subwoofer!
Hope all this helps.
[This message has been edited by Jason J (edited January 31, 2003).]