Subwoofer options for Magnepan with crossover betwen pre and amp?

I'd like to offload the bass below 50hz to a subwoofer through a crossover placed between pre amp and amp; believe this will (a) help with stabilizing the Prima Luna amp by eliminating low bass clipping (b) remedy the lack of weight in the low bass with Magnepan 1.7's. Has anyone found a combination they liked for around $2k? I've seen Vandersteen 2WQ's mentioned, I suppose separate amp/crossover TBD with Magnepan DWM panels are another path. My main concern is a clean merge of the subwoofer with the SQ of the Magnepans