puppyt, don't make life more complicated than it has to be. Just buy another 210 and a good crossover like the JL Audio Or dbx Drive Rack units. Put the subs in the corners like you planned and I think once you get things set up you will be very happy with the results. You can always add more subs in the future but would wager that you will not feel the need.
I personally use 4 subwoofers but I'm forced to to get an equivalent radiation pattern to my satellites which are 8 foot tall ESLs (line source).
People with point source speakers which is the vast majority, can do just fine with two subwoofers in the typical residential setting. One subwoofer is never satisfactory. Those who think it is will change their mind when they hear and feel what two does.
I personally use 4 subwoofers but I'm forced to to get an equivalent radiation pattern to my satellites which are 8 foot tall ESLs (line source).
People with point source speakers which is the vast majority, can do just fine with two subwoofers in the typical residential setting. One subwoofer is never satisfactory. Those who think it is will change their mind when they hear and feel what two does.