You don't list the exact card or motherboard type so it is unclear what media type the card has.
SFP+ slots are backwards compatible with SFP modules. Check the network card data sheet to find what 1Gig modules if any its compatible with.
10GBase-T is typically backwards compatible with 1GBase-T so you should be fine plugging a CAT6 cable from your server NIC into the CCR and it will auto-negotiate to 1GigE. But again you'll need to check the NIC datasheet to be sure. Looking up the Broadcom data sheet is not sufficient as it only tells you what the chip can do not what the card has been designed to do.