High level is the way to go, sub then takes on characteristics of the amp as well. As has already been stated. But I'm sure there are good sounding systems with both methods.
Connecting a sub which way to go
I have a NAD165 Pre-amp and a Nad 365 amp I am connecting a SVS SB13 Ultra into the system. The 165 has a sub output,but is it better to use that or the signal between the pre amp and the amp stripping off the bottom end signals say 15HZ to 80 sending rest on to the amp? The SVS has both a high pass and a low pass filter. The rest of my system is Paradigm S3 V2's and Triad Silver Monitor's