I don't have a specific answer, but I would strongly suggest demoing subs and picking whichever one sounds more musical, regardless of the sub's ability to provide a high-pass output. REL does not feature a high-pass output, but they are very good subs and should not be struck off your list for this reason.
ACI speaker manufacturer offers a passive high-pass filter to go between the preamp and amp (at line level). This would only work if you connect the sub to the preamp at line level, and would clearly not work if you connect the sub to the power amp at speaker level (REL's favored approach).
Lastly I have heard of people getting a very large non-polarized capacitor and connecting in series with the main speakers. Off the top of my head I think you'd need a non-polarized capacitor, rated to at least 100 volts (to be safe) and with a capacitance of around 200 millifarads. Not sure how easy this is to find.
I think it may be best to run full range .. but if you can get the capacitors cheaply try it out.
ACI speaker manufacturer offers a passive high-pass filter to go between the preamp and amp (at line level). This would only work if you connect the sub to the preamp at line level, and would clearly not work if you connect the sub to the power amp at speaker level (REL's favored approach).
Lastly I have heard of people getting a very large non-polarized capacitor and connecting in series with the main speakers. Off the top of my head I think you'd need a non-polarized capacitor, rated to at least 100 volts (to be safe) and with a capacitance of around 200 millifarads. Not sure how easy this is to find.
I think it may be best to run full range .. but if you can get the capacitors cheaply try it out.