a question about x.2 surround

Does a '.2' surround system have to use matching subwoofers? Or, can they be different sizes (and, thus, different ranges)?
I'm thinking of replacing my 7.1 (I have a small room for my HT, so I think it's overkill), and going back to a 5.something. I really like the low end (whether for movies or music shows), and I'm wondering if a 5.2 with differing subs would be better than a 5.1 system.

I've never heard of someone going with a dual-subwoofer setup due to frequency response reasons. Here's a decent article:
 
http://www.svsound.com/blogs/svs/75040195-why-go-dual

drvnbysound said:

I've never heard of someone going with a dual-subwoofer setup due to frequency response reasons. Here's a decent article:
 
http://www.svsound.com/blogs/svs/75040195-why-go-dual

Click to expand...

 
It's a pretty common recommendation among audiophiles. SVS is a great sub company and that 'article' (ad) is a good summary of the audiophile thinking. 
 
Thats not a very common spec, and kind of old to write it in that notation.  Are you sure you arent talking about the newer Dolby Atmos Standards like 7.1.2?
http://www.dolby.com/us/en/guide/dolby-atmos-speaker-setup/7-1-2-setups.html