Is there a possibility to cache one HDD with multiple SSDs?
To my knowledge no. The software for the "Intel Rapid Storage Technology" also doesn't allow you to use more than 64 GiB as cache in the first place. You can "partition" SSDs bigger than 64 GiB to use up to 64 GiB as cache.
The SSD must have "a minimum capacity of 18.6 GB" according to Intel.
Quoting the limitations from the help: