No, AES50 is not supported, only Dante and AVB.
Your board has come with an option card for ethernet and firewire. You can use the ethernet port for a direct connection to a "digital stagebox", which needs to be one of the RM(L) mixers. You can not use any other stagebox or mixer or interface.
All RM mixers come with an AVB option card, so buying a AVB option card for your SL mixer and an AVB switch makes it easy to build up an AVB network. If you want or need to go the Dante road, you have to buy two Dante option cards. As the RM rack mixers are fully equipped mixers, they do not only serve as stage box, but also as monitor mixers. And of course you can use them as stand alone mixers.
