Puerto, 20's and 20.1's always sound better when biamped with an active x-over in my listening experience. I would recommend the Bryston x-over, I use it in my system, which I believe retails for around $2800.00 these days. Also take a look at my recent review of Martin Logan Depth subwoofers, used as a pair, that has brought my 20's to much higher level of performance across the board.
Recommended crossovers for Maggie 20.1s
A number of contributors to these forums have voiced dissatisfaction with the stock Maggie crossover units. So what do you recommend as a replacement that would provide noticeable improvement? The Mye Stands have helped a lot, I could get larger amps (using Krell fpb 350 monos) but don't know a thing about crossovers.