Hi,
If you’re comfortable with BIOS flashing,
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you could theoretically flash the UD3R to support SLI by using the GA-EX58-UD3R-SLI BIOS,
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But you’d still need to purchase an SLI bridge connector if you don’t already own one (or the connector you have won’t fit with the GA-EX58-UD3R).
The GA-EX58-UD3R-SLI mobo comes with the bridge connector in-the-box,
The ball is in your court

Regards