The contemporary computer to receive the old SGI's files needs to have a file system which is compatible with the SGI's file system, and the TSM client needs to be programmed to handle that, where you would use the Virtualnodename option in conjunction with the old SGI's client password to access its data. The first command you should then perform is 'dsmc query filespace' to verify what's there, and then drill into it with 'dsmc query backup'. Whereas SGI has been discontinued as a supported platform in the latest TSM clients, you may need to use an older client level, like 5.1.
Richard Sims http://people.bu.edu/rbs/