Different subwoofer at each corner?

I always try not to put the sub in the corner if it for music. If for HT, it will give the big boom. But for music, you want to get rid of the boom. I would put them close to my speakers. Get them more into the center of the front wall and you should hear a much cleaner bass. Just my two cents worth.

I see, thanks for the input. So the fact that they are not identical does not pose a problem?

PS, they are crossed over at approximately 100hz.

Yes it's true, pull them away from the corners, and closer to your two main speakers. Putting subwoofers in the corner will reinforce the bass alot, but not always in a good way when it comes to music. Also, depending on how deep your main speakers go, you might not want to crossover at 100hz. That is just my opinion, but it is a little on the high side and might color your overall sound, or make it sound sluggish and bass heavy...at least that's what I have found. Try crossing them over about 60hz as a starter. Then move up the xover point a little bit at a time untill the bass seems to blend with the mains. Of course you might be a bass-a-holic? in which case ignore all my advice, crank up the subs, and blow the walls down!

So far my ears are unable to tell the difference

What you hear and like is all that matters.

With more than one subwoofer, proper phasing is important. I mean, there is a potential for the two subs to cancel each other out if the phasing is not right. (Apologies for being pedantic if you already know all this.)

For example, one sub cone could be moving forward during a vibration while the other is moving backward, and the result could be that relatively little bass is actually put into the room.

The cancellation is a function of the input music signals (if they are not identical, like a right versus a left), distance between the subs, and the phase settings on the subs. Dynaudio subs have phase adjustment controls, so after you place the subs where you want, be sure to adjust their phases to your liking.