The VCAs originally used in the SSL were discrete modules made by dbx, but eventually dbx switched to SIP package ICs (2150s) and the modules were built using eight SIPs in parallel to lower the distortion. Then dbx sold the technology to THAT corp, who continued to improve it to the point where today you really don't need to parallel the 2181's in order to get low distortion. I think SSL continues to use parallel VCAs perhaps in order to justify the price tag. Somehow the metal cans increase the perceived value.