The logic 7 is a step down from the Individual audio system offered in the M3. I had the Logic 7 system in my previous 335i sedan and I can say that the system in my M3 has a cleaner sound. The amount of "thump" might be close, but the M3 system does it with less distortion. I think both systems are damn good for a factory stereo.
You also have to look at the equalizer settings and such. Maybe the 135i loaner had the bass cranked up.