Not possible.
Please be aware that there is no single digital amp on the market that can be slaved, from what I know.
Slave capabilities is more an exception than a rule, especially for complex music instruments.
IMHO audio interface manufacturers should provide products with multiple spdif ins and outs, supported with sample rate converters. This would vastly reduce the complexity of cabling and syncing. But either there is no demand, or they cannot see the demand.
In contradiction to the common sense todays sampling rate converters provide a perfect audio quality.