8 sip trunks are not supported. The UC320W can support up to 4 different SIP trunks. Each SIP trunck can have multiple DID number associated with it.
Does your partner actually need 8 different SIP trunks or a single SIP trunk with 8 DID numbers associated with it?
21 extensions are supported, Please confirm how many concurrent calls the customer would need. Of course the appropriate bandwidth would be required to support the number of concurrent calls.