Ok so this would only work with the Y splitter - in the preamp - amp scenario?
Envision it this way: high pass filter INSTEAD of ’Y’ splitters.
FROM the preamp L & R RCA outs
TO the high pass L & R RCA ins
FROM the high pass there will be two sets of RCA outs
one set of RCA outs from high pass will be designated ’sub’ and obviously there will be a set of RCA cables from there to subs. This will be a full frequency signal that will be edited by the sub’s low pass.
The other set of RCA outs will be designated as ’amp’ (or something like that ) and that set of RCAs will go FROM high pass to the amp. It is this set of RCAs that will carry 80 hZ and above (if that is what the high pass is set at).