Dual subwoofers-need to be from same manufactures?

I've got a very large room for my 2 channel stereo and have been thinking of adding a second subwoofer (current one is a Rel Strata III).

Does anyone have any experience using multiple brands? The Rel is pricy for me right now and I'm trying to sort out if I should wait before buying another REL vs a less exspensive brands (or used).
Actually, you could make a great argument for a sub of another brand. A different sub will have different strengths and weaknesses. You can analyze your system for where there appears to be a dip in the bass and buy a sub to maximize that benefit. Or, with a huge REL, a small sub such may be quicker???
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I don't find the Rel lacking, just jave a huge room and would like to enhance what i jave but can't afford to lay $$$$+ right now for another one... Will continue to look for one used on the site.
I'd vote for holding off until you can get two of the same sub.

When I got my second sub, I experimented with a number of different configurations.

I settled on running one dedicated for each channel.
You might also need more powerful subs. Same brand, of course. And I would add same model. Two subs is a more correct arrangement anyway.
Anyone who suggests non directional bass energy should or can only come from identical subs suggests maybe you should get a second opinion. If somebody has 2 quality subs producing non directional energy how can anyone suggest thats the same as main speakers? Can any provide proof you could pick them out in a blind test?
DIY a bass horn then no issues loading a large room.
Why not sell the REL and get a pair of SVS subs? The direct marketing of SVS offers more sub for less money.