We have an MVP210 and we need to increase incoming call capacity from our other 3 sites (they have the same units). Is it possible to add two MVP210's at this location and have the inoming calls hunt through all six ports?

Yes, you can set the VOIPs up to hunt through all the VOIP ports. This can be done by either adding multiple outbound phonebook entries with the same extension or setting the inbound entries to forward the call to another port or VOIP if busy.