Others experience re: subs and Magmepan 20

@imdoc , I think you are crossing over too low and the 3rd order crossover (correct me if I'm wrong) is a bit extreme. I would use something less drastic, like a 1st order crossover (-6db) starting at 70-80hz. If you have a well made powered sub, it should integrate and provide you with the bass you are looking for.
Not to beat a dead horse, that is why the Vandersteen crossover and subs do so well in terms of integration.
@akg_ca , If I, or 98% of the Audiogon readers could afford a $10K sub, then, yes, it might make a difference, but considering the OP has a pair of not quite current Maggies (and I wish I had 'em), I doubt he/she would entertain a pair of ATC C1's.
For comparison, I have an office system with a pair of Hsu VTF-1's paired with Zu Omen bookshelves. The Hsu, in no way compete with a pair of Vandy subs (which I used with a pair of Zu Union). I was blown away when I played music on them with my Atma's. So, using your Janis subs would kind of be like using my Hsu's, but YMMV.
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+1 for Akg. I think the Vandersteen subs coupled with the crossovers will be the best possible combination for your Maggies.
But, since you were asking not for recommendations, but opinions regarding subs, I would have to say that whether ' they feel they got substantial benefit' would depend upon their integration as well as what subs they are using.
Though you can get the low frequencies, you have to remember that those frequencies must be reproduced in a balanced level with your main speakers. Once they stray significantly from a flat response (as well as phase), you loose all semblance of realism. I am sure others can explain this better, but I tried.
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