Hi Donbellphd,
I have owned the KEF Ref Series 104/2 speakers for about 7-8 years and I would say that the bass is a bid shy in this model as it rolls-off around 40Hz. Using test tones from a stereo setup test CD, you really have to crank the volume at 40Hz to hear anything. So, to answer your question I would set the cross-over from the 104/2s to your sub at say 50Hz (possibly higher). Hope this helps.
Kevinzoe
I have owned the KEF Ref Series 104/2 speakers for about 7-8 years and I would say that the bass is a bid shy in this model as it rolls-off around 40Hz. Using test tones from a stereo setup test CD, you really have to crank the volume at 40Hz to hear anything. So, to answer your question I would set the cross-over from the 104/2s to your sub at say 50Hz (possibly higher). Hope this helps.
Kevinzoe