Yes, 4 is the max per card. If your board has a 2nd full length slot, the simplest and least expensive way to get 6 ports would be to add a 2nd card like a GT 610.
I don't see any reason that hub wouldn't work as a pricier, slightly more complicated alternative, though given my unique position I would probably immediately burst into flames if I were to ever recommend an evga product.
If you've got the slot for it though, I'd consider picking up one of these 210s from the clearance section at our online store for $9 w/o rebates:
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