Boy, I hate to disagree with you again, Mike.

Timbre-matching is really not valuable in subs. Our ears can't distinguish well enough to even know where a sub is located, let alone variances in anything but frequency and power. Perhaps if one sub was very slow and imprecise and the other was near perfect (say an SV Sub), you could hear timbre problems. But even then you'd probably notice clearer, tighter bass from one, rather than being able to distinguish timbre issues. And the only effect this would have is to make you want to dump the less good sub, not like spacial issues with non-timbre-matched L/R/C speakers.

There are problems with location of 2 subs, the sound could actually cancel out in certain parts of the room, leaving holes in your room at certain frequencies. Sometimes the best placement is right next to each other, although that sounds weird, it works.

I'm not sure of the price of the mentioned subs, but it's hard to beat SV Subwoofers in any price range starting at $500 and up. www.svsubwoofers.com