Subwoofers for Magnepan 1.7 + Bonus positioning question

Looks like youll need panel amp sub/subs and  use line out from the H400. With that level of amp maybe go with one very good sub for now and save up for a 2nd.

I paired my 1.7i s with Rythmik 400w 12" sub. Only have one for now, but it compliments the Maggies very well. 1.7i s only go down to 40hz, but their big soundstage with even one sub is impressive.

Rythmik subs have servo drives which they say provides a very tight accurate bass. Panel amps have many setting features, sorry I dont think they have control apps?

They have direct to customer sales from TX. Worth a look.

Oh and ixnay with Maggies on subs!

A small pair of REL subs would be a great match--worked very well for my 1.7's that I owned years ago.

NEVER stack Magnepans on anything--it will alter the sound and imaging in a verry bad way.

Definitely a pair of subs, not single, powered, not passive.

Absolutely don't stack your Maggies on top of anything.

I'd like to thank all of you for your thoughts and suggestions. I do appreciate your time. I got myself some SVS sb1000 pro subs and I'm having a fine time trying to figure out all the settings. 

I almost forgot to mention that I didn't stack the Magnepans on top of the subwoofers. Thanks again.

Congrats.  Here are some good basic instructions on how to properly set volume, crossover, and phase in case it’s helpful along with a link for how to do the “sub crawl” if you’d like to find the best places in your room to put the subs.  Hope this helps, and let us know how it goes if you could. 
 

1. Turn the Subwoofer Level control completely counterclockwise to its minimum; 2. Turn the Subwoofer Cut-Off Frequency control clockwise to its highest frequency (i.e. 150 Hz). 3. Set the Phase Alignment Control to 0°; 4. While you listen to a bass music or video selection in your primary listening area, have an assistant turn up the Subwoofer Level control until the subwoofer can be clearly heard; 5. Have an assistant try the Phase Alignment control until you hear the most bass. Your subwoofer and front speakers are now in phase. Do not change phase alignment again unless you move the subwoofer or the front speakers to a different location in the room or move or remove large items of furniture or room furnishings (i.e. carpet, draperies, etc.) 6. Turn the Subwoofer Level control completely counterclockwise to its minimum.  7. Turn the Subwoofer Cut-Off Frequency control completely counter-clockwise to its lowest frequency (i.e. 50 Hz); 8. Slowly rotate the Subwoofer Level control until you match the subwoofer output level with the level of your front speakers. Bass should be clearly audible, but not intrusive; 9. Slowly rotate the Subwoofer Cut-Off Frequency control until you hear the best subwoofer/main speaker blend. If the sound is too ‘thin,’ you have not set the frequency high enough; if the sound becomes ‘boomy’ you have set the frequency too high. Adjust until you find the most natural balance.  The sub should not draw attention to itself.

Sub crawl

https://www.audioholics.com/home-theater-connection/crawling-for-bass-subwoofer-placement