The SL solution involves multiple amps and lost of EQ.
The woofer section of the LX521 requires one amp per driver, just like any other subwoofer. It also uses a LW transform, which is used for most every subwoofer I'm familiar with.
I think the OP is not really interested in going down that path.
You are probably correct. "Wild Borro Betsy" drivers. No further comment required.
Linkwitz makes those drivers work, but it would be so much easier if he simply selected a driver better suited to OB applications in the first place.
Considering he's had Seas manufacture drivers for him to his specs, he's probably using a woofer that's pretty suitable for his intended application. Or, perhaps you know something he doesn't.
