Final verdict with amplifier

Hey all,
I recently posted how my Parasound amp wasn't providing much of an improvement on my Klipsch WF-34 speakers, which are rated at 125W RMS, and 300W peak, and my amp being 205W per channel. Most of the responses that I got was that I needed a decent preamp to integrate into my system. Well recently a buddy gave me his old Carver TFM 55 amplifier, rated at 380 Watts per channel 600 Watts mono, so I decided to give it a whirl. I know that I have to be careful cuz that much power could blow the fecal matter out of my speakers. Well I hooked it up BOTH WAYS. It was slightly better on stereo, and mono was a big difference, but even cranked it didn't harm my speakers. why is that? And how is a preamp supposed to help any of that?