Subwoofer should be close to the plane of the front L and R speakers.
8 feet is likely going to begin to cause some integration issues with main speakers simply because that puts the subwoofer much closer to the listening area (creating uneven sound and making stereo subwoofers a better option)
Group delay is important but this comes from ported subwoofers. DSP is not a significant delay at subwoofer frequencies.
if the subwoofer is sealed then you really don’t need to worry at all
If either your speakers or the subwoofer are ported then you likely will get best results following THX guidelines - sharp cut off filters at 80Hz and therefore minimize speaker and subwoofer overlap. Ports are what usually causes the largest group delays.
Finally your DSP should be able to correct for speaker and subwoofer distances to the listener so that everything is coherent at the listening area.
8 feet is likely going to begin to cause some integration issues with main speakers simply because that puts the subwoofer much closer to the listening area (creating uneven sound and making stereo subwoofers a better option)
Group delay is important but this comes from ported subwoofers. DSP is not a significant delay at subwoofer frequencies.
if the subwoofer is sealed then you really don’t need to worry at all
If either your speakers or the subwoofer are ported then you likely will get best results following THX guidelines - sharp cut off filters at 80Hz and therefore minimize speaker and subwoofer overlap. Ports are what usually causes the largest group delays.
Finally your DSP should be able to correct for speaker and subwoofer distances to the listener so that everything is coherent at the listening area.